First of all you’d freeze as space is very cold. Because the pressure is also very low you’d probably explode – and ‘expand’ into space.
Implosion happens when the surrounding pressure is high – for example underwater.
You would explode not implode as you’re at a higher pressure than space, but that probably wouldn’t happen. No ones really sure but they recon you could survive for a few minutes as long as you got medical attention right away. Your blood would probably boil due to the low pressure. You’d get the bends and various things might explode, like your eyeballs and lungs. What ever happens it would not be pleasant.
You don’t implode or explode, and your blood doesn’t immediately boil as your body keeps it under pressure. Your heart would continue to pump blood around your body, but due to the pressure difference (the vacuum of space) all the oxygen would be sucked out of your blood as your blood was pumped through your lungs. After about 10 seconds that blood with no oxygen in it would reach your brain, and you would fall unconscious. After that your body might swell up a bit, but you wouldn’t burst, and you could probably survive for as long as 90 seconds, provided that you got back inside a spacecraft where there was oxygen.
You also wouldn’t freeze immediately. Space is very cold (-270 degrees Celsius) but since it is a vacuum no heat is lost from the body by conduction or convection. Heat is lost by radiation, but this is quite slow.
You’d also get a nasty sunburn since there would be no atmosphere to protect you.
Apparently you’ll feel the water on your tongue boiling – this was reported by astronauts who were exposed to space-vacuums in the 60’s.
So if you ever have to go for a spacewalk without a spacesuit, remember that you’ve got about 10 seconds before you pass out, and about 90 seconds before you’re dead. Oh and wear suncream 😛