I abused this stuff two times about a month ago. One time at 500mg and then two weeks after the first time I did 250mg of diphenhydramine.

Recently, I took a therapeutic dose of benadryl (two 25mg pills) and it made me paranoid, sensitive to light, fucked up my motor skills, made me feel heavy, restless, and made me have some random muscle spasms.

I was aware before of reverse tolerance but I didn't know it could occur so rapidly and that a month later, even a regular dose would fuck me up that badly.

Will I always have this reaction to anticholinergics or will I ever be normal again?

I also noticed slight HPPD like afterimages, fruit flies that seem to disappear (I am skeptical about this one. Maybe they're real but I am paranoid that they might not be because I always lose track of them after like half a second), and static in the dark.

Another fucked up thing is that I noticed that I seem to occasionally have spasms in my sleep. Not the normal kind that you get when you feel like you're falling until you jerk awake when you "hit the ground". I notice that often I just jerk awake for no reason.

tl;dr brain damage?

I get little twitches in my leg mostly when i take a 200mg+ does of benadryl.

The lesson here is, its ok, but like DXM it shouldn't be done THAT often.

Okay... When you take Benadryl the most common reaction it to is to become drowsy. There are a select few that makes them hyper active, like I was when I was when I was younger. My guess and experience as using it as a sleep aid is that you have a tolerance for it that makes you tolerant to the drowsiness aspect. This would leave you to experience all of the negative effects of it that you usually don't even feel unless you stay awake on it.

I'm calling bullshit on the reverse tolerance from personal experience.