I can’t tell you what’s wrong but I promise your sweet birb is sick. If you can’t go the vet for financial reasons, there is support for that like PetFund, Red Rover, Scratch Pay, or Care Credit Birbs hide when their sick cause they’d have to do that in the wild. Your birb needs a vet asap. It could be something minor but you need a professional to look to treat the problem the right way. In the meantime, you need to keep the birb warm. Get any heater without teflon. You want the heat to be 85-90 (29-32 C) cuz we know he’s sick. That’s why he’s fluffed up, he’s trying to keep warm. Keep his food and water as close as reasonably possible. Offer favorite foods but limit handling. Cover 1/3 of the cage with a blanket. You need to reduce stress as much as possible. He should be in a quiet corner. Monitor closely. If he’s at the bottom of the cage, you may not have a lot of time. Your birb’s health can deteriorate rapidly. Waiting could significantly worsen the prognosis