Few people would say that massage doesn't feel good. In fact, most people would say that massage always feels good. But what about those times that I feel sick or sore after the session? Did my massage break me? The answer: probably not.
Here's the disclaimer: If you haven't told your therapist about a recent injury or surgery, one of your medications, or a condition you have, the massage may not have been a good idea or healthy for you to receive. Your therapist should know when massage isn't healthy (like when you were in a car accident that morning, started a new medication, etc) but you have to tell him or her these things. Barring these reasons, as long as you have a skillful and trained therapist, massage will not be dangerous or unhealthy.In every other case, here's some reasons that you may not feel like the healthiest person alive immediately after the massage:
Muscles are one of the body's storage units. They store hormones, nutrients, some oxygen and other substances. If circulation is compromised in muscles for any period of time, those substances can go rancid or "turn" and become toxins. When massage stimulates the circulation in those muscles, those stored toxins are released into the blood stream and therefore into the rest of the body to be filtered. That filtration takes excess energy, and the body has to "divert power" to the urinary and lymph systems (aka. the filters). That is one of the reasons that your therapist will usually instruct you to drink water after the massage. The water helps those systems clean your blood faster and get rid of those substances.
In addition to the toxins being released (which really is a good thing, I promise), massage also helps your body get rid of stress hormones and release "feel-good" hormones like oxytocin, dopamine, and endorphines. These act as pain killers and help the body feel better, but they can also make you sleepy. If you have been under constant (or even frequent) stress, the switch in dominant hormones can leave you feeling a little "off." In some cases of extreme or chronic stress, the decrease in those stress hormones can leave you with mild withdrawal symptoms like stopping a medication could (though it wouldn't be as severe). In addition to the unfamiliarity, the switch in hormones also causes the body to begin focusing on healing itself, which can leave the rest of the body feeling drained.
Our ancestors had to deal with stress from predators, hunting for food, and other fighting-for-life activities. In today's society, stress is more likely to come from deadlines than deadly beasts or from climbing the corporate ladder than physically climbing mountains or trees in search of food, but the body still responds to all stress in the same way. Stress hormones are released. Blood and energy is diverted from secondary systems (things that the body can do without for a short period of time like digestion, filtration of the blood by the urinary system, and even immune function) to the primary systems like the brain, lungs, heart and skeletal muscles.
Massage, however, helps the body remove itself from that fight-or-flight mode and put more focus on those secondary systems again. If those systems have been ignored by the body because of long-term stress, there may be a period of "detox" as the body is finally able to get rid of the things that had been sitting and going bad. Therefore, it is not uncommon for the toilet to become your best friend for a while after a massage. You may feel nauseous, have mild abdominal cramping, have excessive gas, or even have diarrhea or excessive amounts of stool (think, "when is the last time I had corn?"). These are actually good things, even if it doesn't seem so, because it means that you are getting clean from the inside out, and your body is going to be healthier in general.
Especially if it's been a while since your last massage or you've been under an unusual amount of stress, it's a good idea to schedule your appointment on a day or time that you can rest and relax after the massage. If you can't schedule it for your day off, at least schedule it after you've finished your errands or after work rather than on your lunch break. If your lunch break is the only time that you have, talk with your therapist and see if it is available for you to do shorter sessions more often (like two 30 minute sessions in a week rather than one 60 minute session) to ease your body into massage again.
When in doubt, ask your massage therapist! You two can talk about how you are feeling, and possible ways to avoid those "side effects" of massage.