He knew when the spell failed that he'd lost, and he was slipping away fast so when the opportunity came he tried to nod, not having enough voice to speak and knowing he'd be passed out before his hand could touch the ground in signs of surrender.
The relief of pressure off his throat was immediate, and he felt himself slowly return from the brink of unconsciousness. For a moment, he didn't move, just focusing on his breathing. His hand was still clamped desperately around his wand. He had never lost possession, but he was paranoid, and already knew that at first chance, he'd make sure to disarm Remus. He might even explain why, but he wasn't letting Remus or anyone else take possession of the Elder wand, even if it was stored safely in his vault at Gringotts.