Does heat affect the speed..

My Laptop has been crazy slow recently and i've tried everything including wiping the harddrive and its still slow..

Was just thinking a hour ago that my Vaio laptop was not kicking out as heat from the fan on the side as per usual as if the fan isn't as powerful. so felt the underneath of the laptop and it was crazy hot.

So I put the laptop half on half off my sofa so the fan underneath was blowing out and its a lot cooler... but more importantly it not slow at the moment

Maybe a fan has fooked?

Thats if heat really effects it like I'm guessing?