LOL. Did you really need to make a thread to figure this out?
If you have done any research on mushrooms at all you would know that is a myth. A really dumb one at that.
Mushrooms are extremely benign. It is impossible to die from eating too much mush. You would not be able to eat the amount of mushrooms required to do so.
They do not cause any physical damage to your body at all.
Not at all, apart from the nausea they can produce (because the mushroom itself is a hard material for your body to digest) which is not actually harmful either, mushrooms have no negative effects on your body to speak of. Secondary effects like a pounding heart can be caused by the fact that intense experience occur but again: no direct risks for your body. They are safe.
Furthermore do some research, the answer to this is quickly found in many places.
Next time refer to the Big & Dandy Mushrooms thread for questions that are relevant to it - we have general threads about many common topics! Thnx