Madagascar Swift with muscle spasms

I work at a small mom and pop pet store, and one of our Madagascar Swifts has been having muscle spasms. It's been almost seizure like at times, even. As far as I'm aware he is eating, because the bugs are disappearing, and he has fresh water at all times. I'm not entirely sure how long he has been here, but this is a recent development. Any ideas what could be causing this? Our other swift hasn't had any problems, and they came in together.

Any chemicals been used lately to treat for mites or anything?

No chemicals. I use a 5% bleach to water solution for cleaning.

edit: We use calcium sand, do you think he could be impacted from eating it? I don't know why that would cause shakes...

Still looking for any input if someone has any.

I've started giving her 5-10 minute warm water baths to get her hydrated enough to function. She is housed by herself now and I'm seeing that she hasn't been eating in quite some time. I tried putting some electrolytes in her water every morning, but I don't see her drinking it at all. I've also tried giving her some appetite stimulant/caloric supplement to get her going enough to eat on her own. She won't even take a waxworm; when I got half of it in her mouth yesterday she just spit it out. Today I couldn't get her mouth open at all.

Her seizing stopped for 8ish days, but she started it up again today though not as violently as it was before. I'm starting to think it might be a neurological condition with physical manifestation.

edit: The closest exotic and reptile vet is a boat ride and 2 hour drive away.