Thanks to everyone for your great ideas.

I was definitely wondering about overtraining, but aside from restlessness at night, I have not been feeling generally tired / sick. But it's possible that I need to back off just a smidge to keep myself from going that route.

aicabsolut: good tip about heart rate. Mine is typically around the mid 50s in the middle of the day. I can check in the morning.

Thanks for all the ideas on sleep aids. I have to be careful with those; they make me feel icky, don't seem to work for very long, and sometimes even give me nightmares! So I'm probably not going to go that route.

Tokie -- that's a really interesting idea about carbs. Since going gluten-free, I don't eat nearly as much pasta etc, but I think the night before I started this thread, I had pasta made from rice flour as a "main dish." I'll have to keep an eye on that, see if I notice a connection.