Could you tell me what happens when you leave head lice treatment in your head overnight?

Shampoo: The treatment for lice is usually a very strong shampoo that you then rinse out and comb out the nits/lice. I am not clear from your question what you used. Many people use olive oil and a shower cap over night rather than the rid shampoo because rid is so strong. Basically, shampoo your hair and do not reapply the rid or whichever brand you used for at least a week.