The reboot fixed it. Thanks!
iPads never really go to sleep. I've had misbehaving apps drain my battery while the screen was off for a few hours. I had no idea what the issue was until reading your replies, but I had tried other music programs with midi features, and ALL of them froze. Which seemed odd at the time, because Dropbox, Netflix, even Safari all ran fine. In hindsight, after reading about the bug, I should have just powered it off and back on first, just to see if the bug went away, but there was an iOS update, and I thought, 'two birds... the update will reboot it." I know I was tempting fate, but I started the update and..
Voila! Everything works again.
Thank you all for your responses. The restart was evidently what it needed. I didn't know about the Facebook group, and to be truthful, I'm kinda torn. Facebook has made way more than it's share of privacy faux pas in the recent past, but there are so many helpful and informative people and groups, not to mention keeping up with my geo-separated family members. I'll probably sign up anyway, See you there!