Hi

Greetings from health care magic

Fainting after the injury has two cause 1) Loss of blood causes low pressure and that causes less oxygenation to the brain so he loose consciouness. 2) some persons are hypersensitive of seeing blood and that causes sudden shock syndrome and he got loss his conscouness and micturation.Check his Blood pressure if it is still 80/60 then he may need blood transfusion.

Hope it will help thank you

It occurs because of autonomic dysregulation

it is called syncope that to vasovagal syncope

no need to worry, it is bodies self defence, as a person gets some untoward event
during the episode Bp falls and inturn blood supply to barin decreases

As a result one develops presyncope and syncope

and blood supply to brain is restored

and pt regains conciousness within minutes

thanks for choosing health care magic.Your friend is lucky to have friends like you.See the reason for getting faint is psychological shock of sight of blood.When ever a person comes under stress due to any thing the body starts reading and set of hormones are release inside body and panic button is pressed.some persons like your friend who are sensitive to such thing loose there control and fell down and there blood pressure goes down due to body response to it.After that moment passes off body mechanisms start working and bring back things to normal.But brain remembers the sight which is seen so there is definate picture in mind of a person so some unkwone fear remains and lead to weakness.so do not worry give him something to drink like tea or coffee and ask him to take rest.he will be fine.