Vasovagal reaction: a generalised sensation of discomfort and weakness with anxiety, dizziness and nausea, which may progress to loss of consciousness (faint). Vasovagal reactions are the most common acute complications related to blood donation. Both physiologic and psychological factors may be important. The reaction is generated by the autonomic nervous system and further stimulated by psychological factors. Signs and symptoms include discomfort, weakness, anxiety, light-headedness/dizziness, nausea, chills, sweating, vomiting, pallor, hyperventilation, rapid or a slow pulse, and hypotension.  Loss of consciousness (LOC) may occur and can be accompanied by loss of bladder or bowel control or convulsive movements. Reactions may occur at any time during the donation process including before phlebotomy (rare), during phlebotomy or immediately after phlebotomy, when the donor stands up, or after the donor has left the collection site. Most reactions occur within 12 hours of phlebotomy. Reactions accompanied by LOC carry a risk of injury, particularly if they occur once the donor has left the collection site (delayed vasovagal reactions) (26-30). Risk factors associated with vasovagal reaction have been thoroughly studied and include: female gender, young age, low weight, first-time donor status, and a small estimated blood volume. 
- Vasovagal reaction without Loss of Consciousness (LOC): the donor does not faint;
- Vasovagal reaction with LOC: the donor faints for a period of time;