It is difficult for him to pray qiyaam because of his work situation and because he is a heavy sleeper

Firstly: 

Some of the
Sahaabah (may Allaah be pleased with them) used to do difficult work such as
farming, herding livestock, gathering firewood and so on, but they did not
neglect their prayers, rather they used to observe the prayers regularly,
not just on time but also in congregation. They were regular in praying and
seeking knowledge, and they were not granted any concession allowing them
not to pray because of work. 

Hence it is
obligatory for those who work and others to offer the prayers on time.
Allaah praises the believers who do not let their work distract them from
obeying Allaah, as He says (interpretation of the meaning): 

“Men whom
neither trade nor sale (business) diverts from the remembrance of Allaah
(with heart and tongue) nor from performing As‑Salaat (Iqaamat‑as‑Salaat)
nor from giving the Zakaah. They fear a Day when hearts and eyes will be
overturned (out of the horror of the torment of the Day of Resurrection).

38. That
Allaah may reward them according to the best of their deeds, and add even
more for them out of His Grace. And Allaah provides without measure to whom
He wills”

[al-Noor
24:37-38]

Secondly: 

The one who
sleeps is excused at the time when he is sleeping, but when he wakes up it
becomes obligatory for him to perform the prayer after he has woken up. 

It was
narrated that Anas ibn Maalik (may Allaah be pleased with him) said: The
Prophet of Allaah (peace and blessings of Allaah be upon him) said:
“Whoever forgets a prayer or sleeps and misses it, the expiation for that is
to pray it when he remembers it.” Narrated by al-Bukhaari (572) and Muslim
(684). 

This hadeeth
indicates that the one who sleeps is not accountable during the time of his
sleep, and there is consensus on this point. 

The apparent
meaning of the hadeeth is that there is no negligence in sleep if a person
sleeps before the time for prayer begins or after that but before the time
becomes too short. And it was said that if a person deliberately goes to
sleep before the time becomes too short and he takes that as a means of not
praying because he thinks it most likely that he will not wake up until the
time for the prayer is over, then he is sinning. But the apparent meaning is
that there is no sin on him because of sleeping, because he did that at a
time when it was permissible to do it, so he is included in this hadeeth.
But if he did it deliberately in order to miss the prayer, then there is no
doubt that he is sinning thereby. End quote. 

Nayl
al-Awtaar 2/33, 34. 

Thirdly: 

What a
person should do before going to sleep is to be keen to wake up at the time
of prayer, and to take the means that will help him to perform the prayer on
time. If he does that but does not wake up, then he is excused because he
did what he had to, and “Allaah burdens not a person beyond his scope”
[al-Baqarah 2:286]. That happened to the Prophet (peace and
blessings of Allaah be upon him) on some of his journeys. 

It was
narrated that Abu Qataadah (may Allaah be pleased with him) said: “We
travelled with the Messenger of Allaah (peace and blessings of Allaah
be upon him) by night and some of the people said: “Why don’t you let us
stop at the end of the night so that we may rest, O Messenger of Allaah?” He
said: “I am afraid that you will sleep and miss the prayer.” Bilaal said: I
will wake you up.” So they lay down and Bilaal leaned his back against his
mount, but his eyes grew heavy and he slept. Then the Prophet (peace
and blessings of Allaah be upon him) woke up when the sun had risen. And he
said: “O Bilaal, what about what you said?” He said: “I have never slept
like that before.” He said: “Allaah took your souls when He willed and
returned them to you when He willed. O Bilaal, get up and call the people to
prayer.” And he did wudoo’ when the sun had risen high and turned white,
then he stood and prayed. Narrated by al-Bukhaari (570) and Muslim (681).  

The Prophet
(peace and blessings of Allaah be upon him) took the means of waking up
by appointing Bilaal to alert them when it was time to pray, but sleep
overtook him, and he and the people slept until the sun had risen. They were
not negligent, hence the Prophet (peace and blessings of Allaah be upon
him) said, “There is no neglect among the people.” 

As for one
who stays up all night because of work etc and does not take the means and
prays after the time for the prayer is over, he is regarded as deliberately
not praying, and he is not excused because of his sleep. 

Shaykh
Muhammad ibn Saalih al-‘Uthaymeen (may Allaah have mercy on him) was asked
about someone who stays up all night and is not able to pray Fajr until
after the time for it is over – will it be accepted from him? And what is
the ruling on the rest of the prayers which he offers on time? 

He replied: 

With regard
to Fajr prayer which he delays until the time for it is over when he is able
to offer it on time, because he could sleep early, this prayer of his will
not be accepted from him, because the Prophet (peace and blessings of
Allaah be upon him) said: “Whoever does an action that is not in accordance
with this matter of ours will have it rejected.” Narrated by Muslim. The one
who deliberately delays a prayer until the time for it is over, with no
excuse, will have it rejected, because he has done something that is not in
accordance with the command of Allaah and His Messenger, so it will be
rejected. 

But he may
say: I was asleep, and the Prophet (peace and blessings of Allaah be
upon him) said: “Whoever sleeps and misses a prayer or forgets it, let him
pray it when he remembers it, for there is no expiation for it but that.” 

We say: If
he could have slept early so that he would wake up early, or he could have
set an alarm clock to wake him up, or he could have asked someone to wake
him up, then his delaying the prayer and not getting up for it is regarded
as deliberately delaying the prayer, so it will not be accepted from him.
End quote. 

Majmoo’
Fataawa al-Shaykh Ibn ‘Uthaymeen, 12/question no.
14 

Fourthly: 

A man may be
a heavy sleeper, and one of two scenarios must apply: 

1 – He
sleeps deeply because he has stayed up at night to work, seek knowledge or
pray qiyaam. In this case it is not permissible for him to miss performing
prayers on time because of that, and he should look for another job that
will not cause him to miss the prayers. Similarly it is not permissible for
him to let naafil deeds – even seeking knowledge, which is basically
obligatory – distract him and cause him to miss the prayers. In this case
his not praying is regarded as deliberate, because he could change his job
and he could avoid staying up at night. 

Shaykh
Muhammad ibn Saalih al-‘Uthaymeen (may Allaah have mercy on him) said: 

What our
brothers who go on trips should do is thank Allaah for this blessing, as He
has made them prosperous and given them a life of comfort and ease, in an
atmosphere of safety and freedom from fear, and they should do what Allaah
has enjoined on them of praying on time, whether that is Fajr prayer or any
other. It is not permissible for them to delay Fajr prayer on the basis that
they are sleeping, because in most cases there is no excuse for this sleep,
because they can use alarm clocks to wake them up to pray on time, and they
can sleep early so that they can wake up refreshed. End quote. 

Majmoo’
Fataawa al-Shaykh Ibn ‘Uthaymeen (12/question no.
14) 

2 – A person
may be a naturally heavy sleeper, and it has nothing to do with work or
staying up at night. This is known in the case of some individuals. If that
is the case, then he is excused if he takes the means but does not wake up. 

It was
narrated that Abu Sa’eed al-Khudri (may Allaah be pleased with him) said: A
woman came to the Prophet (peace and blessings of Allaah be upon him)
when we were with him and said: “O Messenger of Allaah, my husband Safwaan
ibn al-Mu’attal does not pray Fajr until the sun has risen.” Safwaan was
with him, so he asked him about what she had said, and he said: “O Messenger
of Allaah, we are a family who are known not to wake up until the sun has
risen.” He said: “When you wake up, then pray.” Narrated by Abu Dawood,
2459; classed as saheeh by Shaykh al-Albaani in Irwa’ al-Ghaleel,
7/65 

Conclusion:
in your case it seems that your sleeping heavily has to do with staying up
at night, and you are staying up at night because of work. On this basis, it
is not permissible for you to stay in that job, because it is causing you to
forsake the most important pillar of Islam after the Shahaadatayn. So look
for another job, and Allaah will compensate you with something better than
it. You will see a change for the better in your religious commitment, your
body and your mental attitude. As for your religious commitment, performing
the prayers on time is one of the most important duties, and not doing it is
one of the worst of haraam actions. As for your body, the doctors have
described many harmful effects suffered by those who work at night; sleeping
during the day does not give the body the same rest as sleeping at night
does. And all of that has a negative effect on one’s mental attitude. 

And Allaah
knows best.