Take it from me, most people have nothing to gain from Diphenhydramine.
It is a peculiar substance, with an effects list it'd take me all night to list; however, most are subtle, and arise with experience.
It is a Deliriant, most of the effects are derived from confusion and disorientation.
Expect flickering shadows, swirling movements in dark corners, a bit of microsleep, possibly light auditory hallucinations.
Effects scale with dose; it has plateaus, similar to DXM. It can cause much anxiety, and restlessness.
My only advice is, let it play; don't resist it, just let it do it's thing, watch it like a movie.
Have you ingested your dose yet?