Solas was ready to be his extra self and sleep right where he was, against the trunk of a tree. Nevermind that he was less inclined to settle down for the night when he spent as long as he had asleep. He's not the one that used all his energy for the day in a summoning ritual then marching off into the wilderness with a supposed 'god.'

"Then why would you believe anything else I say? You summoned me for assistance," he points out. "If you refuse to believe me, you may as well release me from my binding."

Because there would be no point to this arrangement otherwise.