I have been having awful allergies all day (though it may be a cold?) so I took two benadryl. I took them at six, and then felt my allergies coming back, so I took two at ten. They last 4-6 hours. Overdose, or no overdose? So far I feel tired, but that is it. I refuse to look up the side effects of benadryl overdose, though. Because I know that I'll probably start mimicking them, and get panicky.