I guess it can be related, but I have had many deep tissue massages and that has never affected me. but we are all different.
Like they said, drink plenty of water afterward to wash out the toxins from the body. What might have happened is the toxins settled back down on your neck or another sensitive area and the stiffness/soreness directly affected your mood.
Also if the pressure was too deep, a nerve could have been pinched.
Also some people don't care for the deepness but it sounds like this didn't bother you.
So next time drink plenty of water.