This is probably obvious to a lot of people, but I thought it still might be useful since I didn't think of it myself for years. Since sometime in college, I've been the kind of person who wakes up groggily at 10 am and then drags myself out of bed. I've always been a late sleeper so I didn't think much about it, but when I stopped taking allergy pills, I fairly quickly became someone who woke up around 8:30 am without much effort (still not early but not crazy-late).

I was aware that allergy pills make you sleepy, but the actual effect when I take them has never been that strong for me, so I never put together that they might still be having a major effect 10+ hours later. I still occasionally take allergy pills in certain cases, and now that I'm looking for it, it's really obvious how they effect my next morning.

For what it's worth, of the two brands that work on my allergies, 6-hour Benadryl and 24-hour Zyrtec seem to have the same effect on my mornings despite claiming different time-periods.

So, if you take allergy pills and find it very difficult to wake up in the morning, consider trying not taking them for a few weeks. There was a reason I was taking them and this was a minor decrease in my quality of life, but getting 2 more hours of time in the morning more than makes up for it.