It came out before he could stop it, what with the Doctor being right there where he was forming the thought, and it wasn't strictly accurate. He was fucking terrified. Terrified that it wouldn't work, terrified that it would work, terrified of losing something that had been there so long it was practically a part of him now. Terrified of the unknown.
He clung to the chair, to reality, and tried, really tried, to gather himself enough to help.