Wow. This is a minute and a half of serious drama.
From the YouTube description:
James Lee, 25 was taking part in a jump in Wiltshire when just seconds after leaping from the plane he was hit on the back of the head by another skydiver.
The blow knocked him out and sent him hurtling towards the ground uncontrollably.
Luckily two other skydivers noticed something was wrong and chased after their unconscious colleague.
After realising he was unresponsive the two men managed to roll James into a more stable position and deploy his parachute for a safe landing.
It wasn't until James was under the canopy that he began to regain consciousness, he landed safely on the ground with no memory of the drama that had unfolded seconds earlier.
The mid-air drama was captured by a camera on James' helmet.