I don't often sleep in the day, but when I do I often feel unreal/disconnected & spaced out/woolly headed when I wake up, so you're by no means alone. I think it's the transition between the asleep and awake states, particularly if you wake up all of a sudden.
I think you should take the full course of antibiotics if you can stand it Lu. There is some genuine reason you're meant to take a full course that I can't quite remember - not just to help with whatever infection you have, but something to do with future immunity maybe?
My guess is that you're groggy from your nap, which has allowed your anxiety to start to make a root for itself in something this afternoon (e.g. in your worry about the antibiotic side effects). You've been doing so well with ignoring it and getting on with getting out and about recently. This anxiety is no different to what you previously felt about going out; it's just adrenaline. Muster your best hands-on-hips, "don't mess with me" attitude and tell it to sod off - you don't need it, you don't want it, and you've proven that you can get shut of it!
for you, and good vibes!