Can a person in space survive without a spacesuit?Richard Garriott de Cayeux:
You would die very quickly and painfully, but not instantly.
The first thing that would start to kill you would be the lack of air. The air would be forced out of your lungs, and there would be no way to inhale anything. Even if no other problems followed, you would quickly suffocate.
The next very bad and likely very painful thing to happen to you would be gas bubbles forming in the blood and tissues throughout your body. Just as when you release the cap on a soda bottle, and all the bubbles form in the liquid, so it would be throughout your body, all at once and all over. Divers who get the bends from much more subtle changes in pressure describe this as very painful and sometimes fatal. In this case, it would be fatal very quickly, and very painful until it was fatal.
Finally, even if you did have a spacesuit on, you would soon die if you did not have a spacecraft to escape into. Spacesuits must heat you when you are on the shady side of the Earth and cool you when you are on the sunny side of the Earth, as well as provide all the oxygen you need. These systems will run out resources and/or power unless you can get reconnected with a spacecraft in fairly short order.