He was feeling desperation, if Noctis disappeared into the crystal in this dream, would he stay that way? Would he not come back to the ship?

Prompto wrapped both of his hands around Noct's bicep, holding on for dear life.

"Don't Noct...fight it, please, wake up, you can't leave us again, we can't take that-"

He let out a frustrated sound, Ardyn was soliloquizing.

Prompto turned around and snapped. "Don't you ever get tired of hearing yourself talk? Shut up!"

He wasn't ready to face the possibility of Noct not coming back, it was far too soon. He needed more time.