Disclaimer: I am an engineer, not a doctor. I am qualified to tell you how fix your TV (and psycho-analyse you, or read Shakespeare, but that's another story) but nothing else, you take this as you find it. As a first aider, I'm not allowed to give you asprin either; so don't take two asprins and don't call me in the morning.
Before giving up, buggering off, having something to eat, or going to the pub - have a cool down.
Why? cos if you don't it will hurt tomorrow, and the next day, and even all week!
Pain and stiffness is not inevitable, honest. There is two sorts of problems with painful muscle, ligaments, and joints. The first is damage and the second is lingering bad by-products.
A good class will not have a lot of damage, but there will always a bad day (a recent class had around 20% of the class hurt in one way or the other).
The most common is bruising, while this is fairly common try and avoid it (contact should be firm but not enough to bruise). A bag of frozen peas for the swelling and your favourite pain killer (anti-inflammatory). After a week this should be fine, just in time for the next class.
Then there is strained ligaments (and muscles), this come from trying to make a movement more that your body can do. First of all, only take stretching to a comfortable limit and then just a tiny bit beyond. Really pushing will not increase flexiability but will cause damage. The function of streching is to increase the length of the muscle.
This can be achieved by one 30 second stretch, five days a week (Bandy & Irion 1994,1997).
Now this is the result a comprehensive randomised scientific study, so if you disagree with this, quote your scientific evidence and appropriate study. Otherwise can it :)
A strain can take quite awhile to heal; I find a combination of deep heat gels (or tiger balm -note: no tigers were hurt in the production of this cream, or ducks either [I recommend duck oil for stiff joints]), gentile stretching and sports massage works the best.
Finally there is the nasty by-products. When you exercise, toxic by-products are produced (an acid, but I can't remember the name of it). The best way to flush this out is to do some cardio work. i.e. gentily jog and pace around the room. I follow this with a "hot as you can stand" long shower.
Finally, the cool down programme.
Start with a little movement. Often this is a slow walk around the room, followed by a slow jog. Pacing on the spot if you are limited to space works quite well. Do this for around two minutes and take it really easy.
Continue with this a little faster. The most important part of this is that you should not get out of breath (if you are breathing heavily then you are making more toxic byproducts, rather than getting rid of them). This should take about another minute.
Now stretch all the major muscle groups (I'll write this up further when I have a list of these I like).
Finally, lie flat on the floor, close your eyes and relax. Empty your mind, if a thought enters your head just let if flow out again. Do this for around two minutes.
Now get up and shake your arms, legs, and head gentily.
You're looking good -don't quit.