What happens if you leave conditioner in overnight?
Your hair will fall out so make sure you wash it out because its not good for you.
If you leave stew out overnight, bacteria can start growing in it. Depending upon the type of bacteria, certain toxins could also be formed which could make you ill - and in less time than overnight. Illness is not guaranteed, but since you don't know whether pathogenic organisms or toxins are there - it just isn't worth the risk.