Did they remind you to drink extra fluids?

massage and especially deep massage releases so many toxins that you need to flush them out.

I had a massage during PT and felt woozy and disoriented for a short time.
I didn't have a water bottle with me so had to wait until I got home.

But probably the more tension and knots you have the more pronounced the after affects.

Did they pull or press or your head /neck - or twist it much?

Could be partially the delayed symptoms aspect but drinks lots of water and see if that helps.