Hi, welcome to the forum, you may be probably having Circadian rhythm disorders. Due to long term sleep deprivation in night time or delay in sleep will lead to excessive sleepiness, tiredness, loss of concentration and even dizziness.
This usually has happened due to change in normal sleep-wake cycle. Disturbance of sleep cycle disorder can be due to stress, anxiety, depression. Even generalized disease or conditions can cause such symptoms; hence this needs to be ruled out.
Generalized conditions needed to be ruled out are anemia, Diabetes, steroid use, thyroid disorder (hypothyroidism), blood disorder and dietary deficiencies. You need to take healthy food like vegetables, fruits, milk etc with minimum 7-8 hrs sleep.
Firstly you need to undergo routine blood tests like complete blood count, differential count, ESR, Hb% and thyroid profile etc. Also you need to get evaluated for neck disorder which is interrupting your sleep and may be the cause for your problem.
If stress is present, you need to go for relaxation exercises. Appropriate use of sedatives (benzodiazepines) will help you to get adequate sleep. I suggest you to consult a physician and get treated for recovery of normal sleep-awake cycle. Take care and regards.
Im just like that, If I sleep 8 or more hours the next day im really tired. I sleep 3 or 4 hours I feel alert and awake. If you had sleep apnea you would be waking up short of breath. Maybe go to your doctor see what he/she has to say.