Brief Answer:
investigation is required

Detailed Answer:
Hello,

there are various causes to consider and investigation is required. A short list follows:
- not enough rest: either not enough hours of rest or disturbed sleep (for example sleep-apnea syndrome).
- anemia
- electrolyte disorders
- endocrine conditions (thyroid disorders is the most common among them)
- depression

This is not an exhaustive list. I've omitted various conditions like tumors. chronic infections, autoimmune disorders, etc because they don't seem very likely judging by your description.

First of all some elements of your medical history have to be evaluated. Did you have any recent medical problems of any kind?
Do you sleep at regular times (for example at 11 o'clock every night) ?

A bad work schedule may impair sleep. Using the internet late at night might also impair your sleep. Sleeping at a fairly constant time every night might be helpful!

Disturbed sleep is another potential cause. The sleep-apnea syndrome usually affects obese individuals and causes pauses in breathing during sleep. These pauses may result in numerous awakenings, without the patient remembering anything unusual, and extreme fatigue the next morning, like if you hadn't slept at all. Sleepiness during the day is common. Snoring is a sign that you may have sleep-apnea. A sleep study can confirm it.

Anemia is another cause of fatigue. A complete blood count will clarify this issue.

Electrolyte disorders can also be detected with simple blood tests and may cause various symptoms including fatigue.

Hypothyroidism is a common cause of fatigue. TSH measurement is sufficient for screening.

Finally, one of the most common symptoms of depression is inversion of the sleep-wake cycle. Depressed individuals may be unable to sleep at night and feel sleepy (and sleep) during the day.

I hope I've given you some things to consider. They are enough to get started regarding the investigation.
You can contact me again, if you'd like any clarification or further information.

Kind Regards!

---

Brief Answer:
the cause has to be identified first!

Detailed Answer:
A sleep disorder is not serious by itself but it depends on the underlying cause. As I've pointed out in my previous answer, this issue has to be investigated, starting with some simple tests (complete blood count, glucose, urea, creatinine, TSH, etc) and perhaps also a sleep study.

In the meantime try to go to bed at a regular time and avoid strenuous physical activities before sleep. Avoiding prolonged internet use before sleep may be helpful too.

Kind Regards!

---