Benadryl has been used as a non-habituating sleep aid for at least several decades. All of the OTC sleep aids contain Benadryl (diphenhydramine) as the active ingredient for sedation (Sominex, Tylenol PM, etc). The only problem is that with regular use, you develop a tolerance to the sedative effect. Plus, antihistamines are very drying to the mucous membranes, so if you are prone to dry eyes or dry mouth, definitely not a good choice. Some people get over sedated with it and have a hard time shaking the groggy feeling the next day. I don't know what is worse, groggy from over sedation or groggy from not enough sleep...
That said, during my early post op days, I did take Benadryl frequently to get more than 3 hours of sleep at a time.
Jan