@MAmom111 I am so sorry your kiddo is dealing with this. I wanted to share my daughter’s experience with something similar in case you can take something helpful from it.
I also have a rising senior – the very first week of freshman year, she got Covid. It wasn’t terrible, but she was moderately sick for about a week. Just as she was getting better from that, she started waking up with what you describe – extreme nausea and chills, and when she tried to stand up, she’d feel lightheaded and turn white as a sheet, and a couple times she passed out.
We tried all kinds of things, but nothing worked. Interestingly, a couple hours later, she’d feel okay and be ready to go to school. I can’t count the number of times I drove her to school late that fall. She’s a marching band kid, and she hated the idea of missing rehearsal and games, so she’d push herself to get to school by 10 a.m. (which is required in order to participate in after-school and extracurricular activities). The school principal once called her out for pretending to feel well just so she could do marching band. Not to mention, she was in some rigorous classes that fall, and she had to keep up. It was a mess.
Oh, and the kid lost her appetite completely – she stopped eating and lost an alarming amount of weight.
This went on for months. The pediatrician ran all kinds of tests – we visited repeatedly – and found nothing. Finally she referred us to a GI who also ran every test (yay for stool tests, lol) – and finally diagnosed my kid with “functional symptoms” because she didn’t find a single thing wrong. She explained to us that it’s very, very common to see this in kids following a virus (like Covid), where the body recovers, but the brain still thinks you’re sick.
As a treatment, she prescribed cyproheptadine (I see you’ve already tried this with no luck) in hopes of increasing my daughter’s appetite. And then, she told us to buy an OTC med called FDGard, which is for indigestion.
Well, the combination of those two things worked. Within two weeks, she was nearly back to normal (after MONTHS of this happening every morning). She stayed on the cyproheptadine for a couple of months, but I don’t think she needed it for that long. We were so happy to see her eating again, though.
I’m still not sure if those two meds did anything, or if they served as a sort of placebo effect.
Couple more things – one, you can find anti-nausea music online. I found some music on YouTube that I used to play for her when she felt awful, and she said it was somewhat helpful. She liked this one – https://www.youtube.com/watch?v=d34oPW0RQyY and this one – https://www.youtube.com/watch?v=hMZGZUgdT54&t=10282s (that second one is really soothing). There are many different ones if you search for them.
The Relief Band is also something to look into. (You might have this already?)
Here’s the thing – my daughter also has ADHD and anxiety. She was taking ADHD meds (Concerta) on school mornings that fall, but we stopped that while she was feeling sick. It didn’t seem to affect the nausea either way. (As an aside, my son has been taking an extended-release methylphenidate since he was very young, age 5, and last fall, at age 17, it started to make him really nauseated. We tried different meds, different dosages, breakfast, no breakfast, etc. Nothing helped, and he decided to stop taking it for good. I don’t love this because he still very much deals with ADHD, but I haven’t been able to convince him to try again.)
The anxiety hadn’t been officially diagnosed at that point, although we certainly knew she was an anxious kid. But she started having trouble with panic attacks the following summer (the nausea thing was many months in the past at this point), and she was diagnosed with three different anxiety disorders – general, social and panic. The doctor prescribed an SSRI, and after some trial and error, we found one that has been life-changing. No side effects, just a happy kid that is able to keep her anxiety at bay. (She also had many sessions of CBT and learned some helpful techniques, but she mentioned to us that the meds worked so well that she didn’t have much need to use the coping strategies.)
Anyhow. It does seem like anxious people are more prone to nausea – but, I’m hopeful in your son’s case that they’re able to pinpoint something specific that they’re able to treat. Wishing him the best!