Sucked up foxface

[gws294]

I have a relatively new foxface (about 4 weeks in my tank) that up until now has been eating well. He still looks a little thin but moving well and so forth. Tonight I lifted the hood to check something and I noticed him sucked flat up against the overflow grating. He was absolutely motionless. I was bummed. went to get the net to get him out of the tank to give him the big flusheroo and he takes off across the tank.

Is this behavior normal ??? or am I about to lose this fish??? Was he just sleeping in the current of the overflow???

Thanks for any insight.

Geoff