I need complete history before answering your question. Do you have Diabetes (Raised blood sugar)?, Do you snore at night during sleep (Called sleep apnoea)? Most likely cause is snoring resulting in stoppage of respiration hundreds of times during sleep, and wakening you unknowingly. this results in lack of sleep at night brain functions and chemicals are not restored to normal level and you feel sleepy and tired during day. It may be dangerous to drive because it may result in momentary drowsiness resulting in accident. you must under go tests under sleep medicine specialists available in large tertiary Hospitals.