I had the very same problem a few years ago and once fainted after getting out of the bath after feeling a bit weak. I thought it was funny at the time and did not think much of it until I accidently told my therapist who was concerned that there was something seriously wrong with me.This made me laugh even more but he was 'not amused' Hahahah I eventually mentioned it to my GP who said it was an extremly common side effect of having a bath or shower which is too hot. The blood rushes from the brain to the blood vessels in the skin (capilliaries) to cool us down and this can cause feelings of light-headedness and fainting.