My beardie is a 2yo rescue who started brumation in early December. Once a week I wake her up for a bath so she stays hydrated/in case she needs to go to the bathroom.
Today she started shaking while in the bath. It didn't look like twitching/tremors but more like a person shivering because they are cold. When I lifted her out of the bath she "shivered" for maybe 15 more seconds then stopped.
I have not seen her shiver outside of the bath. She almost launched herself out of the bath (using all four limbs) so besides brumation sleepiness she seems to be perfectly capable of normal motion.
So what happened? Was the bath water too cold? I don't have a water-proof thermometer, usually I make the water about what I would find comfy for a shower. I've bathed her 10-12 times since bringing her home and this never happened before.
I am a little worried about MBD; due to brumation she has not been eating or basking.
The change in temperature for the water may have startled her. I'd make the bath water just slightly warm to the touch which would put it around high 90s or low 100s. The baths shouldn't last more than a few minutes and you should dry her off thoroughly and let her bask afterward to warm up. It's natural for them to brumate. They shut their systems down so they don't need much food. I suggest monitoring her weight. It should remain relatively stable. A small (% wise) drop is OK but a significant drop in weight may indicate another issue. If her weight is stable she'll probably be just fine.