Wow, thanks so much for all the replies, everybody!

It's helpful to get other people's perspectives because when I'm thinking about it on my own, I just get more and more worried.
It's been happening to a smaller degree every night now. So, this is my new nightly "normal"--waking up shaking and having the urge to go #2. I also seem to have to go #1 more than usual. I'm exhausted because I can't get any sleep what with all the shaking and running to the bathroom.
Responding in a general way to some of what people have said:
I do think I have adrenal fatigue, so maybe that's what's causing this.
I've been gluten-free for 2 months now.
I do have mercury issues--I think--at least, I have lots of mercury dental fillings.
Thank you, Wu Wei, for listing all the possible things that could affect my mercury problem. I have been eating way more coconut oil the last couple of months (trying to cut down on dairy). I've also eaten some homemade fish broth and seaweed, which are probably both high in iodine--but only about once every 2 weeks. I have been eating very small quantities of fermented vegetables occasionally, so I guess that's probiotics.
Could all this be from the coconut oil? Is coconut oil basically dangerous if one has amalgams? Lately I've only been eating perhaps about 1 tsp a day of coconut oil, but a few weeks ago, I was eating more like a couple of tablespoons per day.
Are the vitamin C, selenium, and magnesium stuff I should avoid or stuff I should seek out to help with a possible mercury stir-up? I've been taking magnesium occasionally to help with insomnia. I plan to eat some lentils tomorrow.
That's interesting about diverticulitis and IBS. I'll have to look those up and see if I have any of the other symptoms.
I know I should go to a doctor, but I don't have health insurance, and I actually don't even have a regular doctor.
I'm still wondering if ibuprofen could have a delayed side effect like this. I took my last dose 3 days ago (took it for 4 days in a row). But last time I got this weird shaking thing, it had been a whole week since I had had ibuprofen.
Thanks, everybody!