@vargo4078 Argentine tegus DO brumate contrary to what places like the major pet stores will tell you. This info gets messed up because MOST Columbian tegus do not brumate. But if you have a black and white Argentine, chances are, he’s just doing what is natural! 
They can start brumating behaviors as young as a year old. But as always, you should consult your exotic veterinarian and make sure it’s not an illness. Do some research on brumation if this is your first time hearing about it. Should put your mind at ease a bit. lol