Well, ok. So I overslept. But I blame my alarm clock!
I got pretty drowsy at around 4:20 am, so instead of waiting 'till 5 like I'd planned, I decided to take my nap a bit early, and set my alarm for 5:05 (since I'm planning to stay awake in 6hr blocks, I decided to get 45mins of sleep each time, for a grand total of 3hrs per 24hrs). Anyway, I awoke not at 5:05 but at 7:39, oversleeping almost 3hrs. But my alarm clock was still on! (though it wasn't beeping when I awoke)
I'm pretty sure this alarm does not go off by itself. So it should have still been beeping when I awoke, though I can't be certain. Plainly it either malfunctioned or I did. I don't remember it beeping, and I certainly did not turn it off. So it must have gone off, if it worked, and I must have slept through it. And if it didn't work then I'm happy to have only overslept 3hrs. Well, the vibrating alarm I bought yesterday should be arriving in the mail any day now. So hopefully that'll manage to wake me, and do so without disturbing those around me.
For now I'll just treat this as my core sleep and try to proceed with my other naps as usual. The question is when to take my next nap. If I hadn't overslept I'd take my nap 6hrs later at 11am, except that I was trying to move my schedule up a bit to be in sync with school, so maybe at 10am. But now I only have 2hrs 'till 10am. I think I'll still nap then, otherwise I'll have totally screwed my schedule up.