typically brumation can be brought about by reducing daylight length and temperture gradually over a month, about an hour a week and temps about 5 F till you are down to 10 hours day, 14 hours night and basking temp 90F or so with ambient temps daytime around 70F and nighttime temps to whatever room temperature you have.
when my dragon brumated, she did it on her own, mostly because the house temperature dropped significantly during the early winter months. the apartment had horrible insulating and heating costs was high so i didn't keep it above 68f. my bearded dragon took this to mean it was time to brumate and went to sleep of her own accord. i reduced lighttime hours to 10 and changed the basking light from a 125 w flood light to a about a 75watt so it would not get too warm in the tank.
as your dragon is already in brumation,but is loosing weight fast, when they shoudl loose very little weight during brumation. i would bring the daylight back to 12-14 hours and the basking temp to n ormal, 95-115F. in the morning, bring him out of his hidey hole, after the lights have been on for about an hour and put him on his basking spot. give him some time to warm up then give him a bath to help hydrate him. once he seems alert, offer some mixed greens and a few crickets. if he doesn't start to perk up and eat more normally, try adding some pediatrilite [or however that's spelled] or gaterade to help restore lost electrlites from dehydration. some low fat non sweetened fruit yogurt can also be offered, to h elp get the beneficial gut flora going again. if he continues to remain lathargic or suffer rapid weight gain over the next couple days, a vet check should be done.
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PHLdyPayne