What happen if i sleep a lot?

Generally - not much: A night or 2 of "banking" sleep or repaying "sleep debt" is harmless\helpful. ? Is why would one sleep "a lot". Has one developed an increased sleep need, a disorder called hypersomnia? Mood disorders, medications, primary medical or sleep disorders, work, school, play schedule, other dysfunction can be at fault. If it is new or a "problem" talk to your doc about it.

Sleep Apnea: If you have symptoms such as insomnia snoring hypersomnia excessive daytime sleepiness obesity asian race cognitive deficits mood disorders htn etc increase the chance of sleep apnea rule out other causes, could be medical, genetic long sleeper etc.

Worst case: death: There have been case reports of people who have died because of lack of sleep. You are also at higher risk for accident / injury from lack of sleep. There are higher risks of obesity, of school problems, attention difficulty, mental health issues from lack of sleep.