Bloodletting

I think you're talking about bloodletting which is a traditional naturopathic method for dealing with mental and physical problems. It's considered a preventative and a form of detoxification esp if you have fatigue, high blood pressure, depression, high cholesterol, allergies). I'm sure it would help with candida and parasites and anything that means you may have 'dirty' blood.
It usually only involves the loss of a small amount of blood (about 1/5 of the amount given at a blood donation).
Certain rules must be followed eg
letting the blood flow freely
bloodlet between 3-5 fl oz
should take place on an empty stomach
should take place at certain times of the month in accordance with the moon
should be carried out once a year at the most preferably in spring.

This info is taken from Moon Time by Johanna Paungger and Thomas Poppe

I personally wouldn't donate blood as they take too much and I'm iron deficient and people should take this into consideration. I have noticed feeling better (brain fog cleared) about 1 hr after giving blood for a blood test on 2 occasions which I thought was really interesting. I don't believe it was psychological.

Anne