Why does my laptop turn off during sleep mode?

Hi! Forgive me for not knowing a lot of technical terms, but I'm going to try to describe what's been happening. My laptop has been having trouble when it's in sleep mode. Normally, when I close the lid, it goes to sleep like it should. One of the two power lights go out. However, sometimes I'll check back sometime later to see that power light back on. I lift up the lid and my laptop acts as if it has turned off and turned back on as all my windows are closed and it's extremely hot as if it's been awake for a while. The fan is going as if it's on, as well, even though it should have been sleeping. Can anyone help with this problem or at least maybe explain to me why it's happening? Thanks!