Check to see if the vents for your PS3 are blocked or clogged in any way shape or form. Be sure that your unit is in a place in which it has free ventilation and is away from other sources of heat. It's also possible that the fan(s) within the unit have stopped which would result in the aforementioned overheating. 

P.S. You mentioned that your brother used it correct? Ask him if it was acting weird or overheating for him while he was using it. In general though, if it's been in use for a while it's generally a good idea to let it cool off before starting another session.

That's kinda funny cause i never had a problem with my PS3 ever until my brother started using it and then it began to freeze on him requiring a reboot.