Hypovolemic shock after blood donation?

Is it possible for a healthy adult who donates 500 mL blood to get into the (compensated) shock with pale, cool and sweaty skin? I mean, does anyone know if this has actually happened to someone?

Also, is it any quick and reliable test to differ between hypovolemic shock and vasovangal syncope?
Symptoms of both seem to be similar

Authored By Jan Modric on Monday 18th November 2013