caffeine makes me sleepy?!

I've long felt that caffeine had no effect on me. Thought that perhaps it was because I had too many sodas as a child or something. But over the past few months, I've noticed that a cup of coffee at work, rather than giving me a boost, makes me more drowsy (and I don't mean after any sort of sugar high). I didn't think much of it until last night.

I'd gone to Starbucks and gotten myself a Pumpkin Spice Latte (very good) whilst I tried to stay up with Kant. (he and I aren't getting along so well, but I'll keep trying) I got home and was reminded that Lexi had asked me to take her to the airport at 4 in the fast-approaching morning. She advised, "So don't stay up too late!" I was thinking, yeah sure, even if I don't get a boost, it's sure to keep me awake, right? It occurred to me shortly thereafter that it was about 10:30 and I was already getting very tired, having almost finished my drink.

So I did a search: "caffeine makes me sleepy" and read bits of a few of the different hits. This one I read all the way through: "Why Doesn't Caffeine Affect Me?" Just a forum discussion, but I was intrigued. It's not all in my head? It might actually make some people drowsy? Weird.

So I didn't stay up too late - I was too tired to. I woke up a good bit earlier than the 3:50 I'd set my alarm for, but I imagine that was because I was worried about not waking up on time. (a common occurrance for me) Then I had some errands to run (long story... but I'd rather stay up late and do them than have to wake up early to do them before work) and got home at 5:00. I had some difficulty falling asleep again, but I was able to get a few hours. Hardly what I would call a good "control" night for an experiment, but notable.

Can anybody relate to this? Should I be having a cup of coffee rather than wine before bed?

side note: I drank a cup of coffee black for the first time on Monday. It was definitely a new experience for me and bears looking into. (thanks go to the friend who offered it to me!) I likened it to eating 80% chocolate, which, if you've never tried it... be warned. It is not for the faint of heart. (Btw, it was about 7pm at the time. I didn't notice any lift or drag due to it, but it certainly had no negative effects on my attempts at sleep come 2am that morning.)