Do you fall asleep but still wake up tired and dizzy? You might need to be checked out for Sleep Apnea. People with Sleep Apnea often do not get enough oxygen when they sleep which could cause them to feel dizzy or have bad headaches in the morning, also you never really go into REM sleep so you are exhausted all of the time. I definitely would talk to your doctor about it though even if it does not sound like sleep apnea to you, it could be some other problem.
It could be different things. Mostly common is eating habit/diet. Some foods can cause lack of sleep. Also, another thing is your surrounding, like tv, radio, etc.. Anything with light... Especially your cellphone. You should try sleeping on a certain time everyday for around 6 hours. Sleeping at random times will make you feel horrible in the morning.
Get both a daytime and nighttime sleep study done. I found out that way I suffer from insomnia and a daytime sleep disorder causing excess daytime sleepiness. So I sleep in the day then can't at night.