Having a massage, especially a deep tissue massage, is a form of passive exercise, as hard as that may be to believe, and you need to take care of yourself as if you have just exercised.
You don't want to ruin that relaxed high you're on right now, do you? Since you were too relaxed to hear me, let me give you some information and rules to follow.
Drink Lots Of Water, Especially For The Next 24 Hours - this is perhaps the most important rule of all. Rehydration is key to a healthy body, especially after a massage. Since massage promotes lymphatic movement, drinking water and hydrating yourself is key to moving toxins through the kidneys and out of the body. Drinking water is the best way to do this - and no, water in tea, coffee, soft drinks don't count! Don't be surprised if you seem to have an increased urine output, i.e. you are peeing much more. This is also normal.