Maybe, what was monday? When was your last chest workout?
There is a balance between training frequency and volume, as well as intensity thrown in there, so dont overdo it thinking you are shrinking. Growing takes time, thats just the breaks.
Do you measure yourself? I typically measure the arms and waist only, if my arms are growing everything else is too, and vice versa. Outside of pump though, even a 1/8 inch decrease would be pretty severe, and that would be hard to see dissapear.
I think its your imagination or you are seeing after effects of the workout itself. My back looks MUCH fuller during a workout than at any other time. Over the 2 hours following the workout or so the "pump" slowly goes away.