Just today, my beardie started acting very lethargic. All she does is sit around, and when I offer her food she seems to be uninterested. I also see her rubbing her nose up against the glass. She is in a 40gal breeder with a 100w heat lamp and a reptisun 10.0. She is 9 months old and is feeding on superworms.
she could be starting brumation if she's sleeping more often than normal... it could also be impaction, and it could be parasites... not to scare you, but it could anything really, a lot of beardie aliments have similar symptoms. if she is acting stranger than usual that may help give a clue to what's going on. i'd keep an eye on her to see if she gets any better or worse, but keep me updated on how she's doing!
Do you see signs of a shed? That could put her off her appetite. Have you tried taking her out of the tank to let her roam around (supervised)? She also may just want out so she can explore and burn some energy.
Have you replaced the reptisun 10.0 recently, they are only good for 6 months as the phosphors decay over time resulting in a decay in the UVA and UVB flux emitted.
Is it a compact (and it's wattage) ?
T8 ?
T5H0 ?
how far from the basking spot ?
Under or ontop a mesh lid ?
Often sudden lethargy is due to inadequate UVB light or improper temperatures, so as Knobbys already asked, which Reptisun 10.0 do you have, a long tube or the compact? And what strength, a T8 or T5HO? How old? And is it sitting on top of a mesh lid? How far is it away from his basking spot?