1. YOU WON’T EXPLODE
Even without a spacesuit, your skin can resist a pressure difference of one atmosphere, so you won’t explode. Don’t hold your breath though, because without the atmosphere pushing against your chest, the air trapped in your lungs will expand and rupture the tissues inside, forcing air into your chest cavity and blood, like the worst case of the bends.
2. YOU WILL ASPHYXIATE
Since you aren’t holding your breath, you have 15 seconds before you lose consciousness, or as few as five seconds if you are panicking. If you are rescued and restored to normal atmospheric pressure within 90 seconds, you have a good chance of making a recovery. But any longer than that, your heart will stop and even a defibrillator won’t save you.
3. YOU’LL FREEZE DRY
In the vacuum of space, water will boil even at body temperature, so the moisture in your lungs, mouth and eyes will boil away a few minutes after you die, eventually drying you out like a mummy. And with no ozone layer to shield you from the Sun’s UV radiation, your desiccated corpse will char black over the next few months.