I take 4-6 a night in order to fall asleep at a decent time, so don't worry, you'll be fine OP. That said, diphenhydramine has recently been understood to potentially contribute to Alzheimer's/dementia so you may or may not lose your mind when you hit 75+ years old.

https://www.health.harvard.edu/blog/common-anticholinergic-drugs-like-benadryl-linked-to-increased-dementia-risk-20150128812

Also, don't use it to get high unless you want to start seeing millions of spiders crawling on your walls, hearing things and other shit. Deliriants will give you the most fucked up hallucinogenic experience. It is not a good time.