Ok you want 2 digital probe thermometers - place the probe on the spot he sits for basking 10 min or so get the temps-- stick ons are good for ambient temps
I use a dimmer switch on a halogen bulb for the heat source, and if it helps, I created this video for my pet sitter to show him how to check temperature using the gun.
If any of this is not accurate @KarrieRee please correct me
To get the temp up a little for now you can put tin foil on top of the tank however you probably need to change the bulb. Youu need a 100W or a 150W bulb. I use the flukers basking bulb, that is on Amazon. But there are more options. I will put some links below. Exo Terra Sun-Glo Daylight Halogen Lamp, 150-Watt https://a.co/d/bTPu2zr, Fluker's Basking Spotlight Bulbs for Reptiles https://a.co/d/bc73ktB, Zoo Med Reptile Basking Spot Lamps 150 Watts (4 Pack) Amazon.com. These all have 100W options on Amazon I believe.
The primary thing needing to be changed would be your lighting for the UVB. That is most likely
what is causing that type of behaviour & jerky movement. He isn't able to process his calcium or
other vitamins/minerals. It looks neurological.
Are you using the digital probe thermometer to measure the temperatures during the day?
This happened suddenly?