Just anecdotaly my dad is/was having some health problems. he got to the point he couldn't carry a conversation and couldn't walk in a straight line without falling over.
He finally told me he was taking benadryl packaged as one of the OTC sleep aids, but taking it nightly for months or years. Once me and his doctor convinced him to stop he improved like 400x better within two weeks. He never noticed a difference.
I only knew it was a problem because I took large doses in highschool and his symptoms seemed similar once I could connect the dots.
I'd imagine it's because of how many instances it's gone excommunicado with.