Thanks for the additional input, especially the good doc's warning to cyclists about heat exhaustion. Now things are coming into focus for me. I only use benadryl to sleep at night, which is a totally different situation from cycling; and I always try to stay well hydrated in the mountains, even more so if I am ingesting any medication, Rx or OTC, since they are usually metabolized/evacuated by the liver and kidneys. Also, I usually take only 1 x 25 mg a night, maximum 2 x 25 mg. I would guess that, based on my lack of negative side effects, my body is clearing the benadryl or its metabolites by the time I start hiking the next morning?? So far, so good, I guess.