Notes on diphenhydramine as a sleep aid:

There are two major points to remember when dealing with using benadryl to get to sleep. First, it is extremely potent, and a fairly small dose will knock out just about any "normal" case of insomnia. The second point is, for all of that, it is not a good way to get to sleep, even on an "emergency" basis. Even on an emergency basis, usage is never a good thing.

If you read the above writeup on the "recreational " use of benadryl, you will see some of the reasons why it is not a good idea to play around with this substance. Of course, at the doses used to cause sleep, it is not causing 24 hour long blackouts, but I have experienced some hypnogogic hallucinations while under the influence. A metallic taste in the mouth and difficulty in micturation can also be expected. Of course, for the person who really needs to sleep, sucking on some cast iron lozenges is a small price to pay. But this comes to the Catch-22 of diphendhydramine. Whatever you gain in time spent sleeping from the effects, you lose from suffering the weird hangover the next day. Four hours of straight sleep are probably going to be about as refreshing as 8 hours of drugged sleep.

If, for whatever reason, you choose to use Diphenhydramine as an emergency sleep aid (and that is about all it is good for, since it developes a tolerance quickly), there are a few things to remember.
First, it doesn't make you sleepy, it makes you drowsy. If you are already fairly well caught up on sleep, and haven't been awake for very long, there is a good chance that it will leave you droopy limbed lolling insensitate, without actually causing you to sleep. After a few hours, the effects may wear off, and you will still not be asleep.
Second, be careful with the dosage. It has a way of creeping up on you slowly. It may take a long time to onset at all, and then once it does, increase very quickly. Don't start popping pills if it doesn't work at first.
Third, it does not give especially respectful sleep. I've noticed some rather odd nightmares under the influence. If you are in an unfamiliar situation, you may be disoriented when you wake up. Prepare for this.

I would suggest other remedies for sleeplessness, such as hot cocoa with honey and soy milk, and apologizing to the people you offended.