Why do sleeping pills seem to keep me awake?!

Diphenhydramine is known to cause paradoxical reactions in some people. This happens mostly in children, but can happen with adults also. What this means is that it actually makes you more awake, alert, and even possibly hyper. It is also possible that if you have been using it long term at high doses (500 milligrams is a huge dose) you may have developed a tolerance (and by the way, in this situation, the correct term is "tolerance" not "immunity". Immunity is what happens when your body is unable to contract a disease because you already have antibodies to fight off that disease. Tolerance is what happens when your body becomes adjusted to a medication and it no longer works for you). Try a different medication and see if that works. Doxylamine is another antihistamine with powerful sedative properties, and it is often said that it is even more sedating than diphenhydramine and even phenobarbital. Unisom is doxylamine. Be sure you get Unisom that comes in tablets, as the original Unisom formulation is just diphenhydramine and comes in gel caps. Check on the back of the box and look at the ingredients to make sure the product you are purchasing is doxylamine and not diphenhydramine. There are probably generic forms which are sold by the chemical name doxylamine. Just check the ingredients on the back of the box to make sure you are getting what you want. You will find it on the shelf along with other antihistamines and cold/allergy remedies.

drink water with the pills and please don't take a overdose. Btw the 1st guy who said your body is immune is correct. You are now use to the sleeping pills and it no longer gives you a drowsy affect

its an older sedating antihistamine and the amount of sedation varies from none to a lot, depending on the person, also you could lose sedation eventually by getting used to them

Your body is probally immune to the medication.

it's called a paradoxical reaction to a medication.