I just bought some Nytol (Diphenhydramine) as I have been having trouble sleeping the last few days. I have an exam early tomorrow and my plan was to take some if I can't get to sleep tonight. My main concern is that the half life is around 12 hours. That surely means that half the drug could still be in my system during the exam. Does anybody know what affects Nytol has the morning after? I could always go get something herbal but I always doubt there effectiveness.