Consequences of Hatha Yoga

It's been a long time since I kvetched, so here goes:
On Saturday morning I ventured out and into a Hatha Yoga class. I had stopped doing yoga for years because, my dear readers, I have a lower back pain injury, which I believe was caused, among other things such as terrible posture, sitting too long in front of a laptop, and no abdominal muscle tone, by a yoga class where the abominable teacher insisted we could all become human pretzels. Well, she didn't know me. But, boy did she screw me up.
I have been fighting this pestering pain, which is like a nagging visiting relative who decided to stay for good, for at least 5 years. I was told "no more yoga for you". But as I'm currently under the apparently unattainable quest to lose a bunch of pounds, I decided to give Hatha a crack, since this form of yoga is the one where you stay in the different positions, as opposed to running from one to the other as if someone was trying to set you on fire. Moreover, it is the yoga that my beloved aunt Dora practices and recommends.
Well, to make a long story short, it was grueling. Today, everything aches. But I expected my lower back pain to pulsate with a vengeance the next day, and so far it hasn't. I don't know if I am so sore all over that I can't even feel it, and yet it is there as usual; or this crazy feygeleh teacher (who actually had a very delicate touch) did something that actually took my back pain away. If this is indeed the case, wow.
Anyway.
The other thing that happened is that I seem to have caught some kind of sleeping malady. I am beset by sleepiness and I haven't been up that late. I just woke from a nap from which I could not wake up. Are these things connected? Did my body get such a thorough workout that now all it wants to do is sleep? Hmmm.... If anybody has an answer, please chime in.