I added an underwater camera to my setup a few months ago and it's been super useful. I rigged it near the back of the tank for a better view of the bottom dwellers I usually miss.
Motion detection works fine even underwater, and night vision is decent as long as there's a small light nearby...
I just pointed my indoor cam at the tank from a shelf across the room and it works fine for checking in. Motion alerts are a bit too sensitive for fish movement though.
Keep an eye on it and monitor your turtle's behavior. If it worsens or if your turtle starts acting differently, it might be wise to consult a vet for a closer look. Also, you can find some tips about it at https://www.tortoiseowner.com/. I hope your little friend gets back to normal soon!