Why do some people feel strained or dizzy after blood Donation?

Hi there,
There are so many reasons for this "dizziness" after donation. Following are the main.
For the ideal healthy blood donation, the weight need to be minimum 50 kg, Haemoglobin 12.5gm%, Blood pressure not lower than 100/60 and not above 150/100. Any deviation anywhere , in any of these parameters can lead to "uneasiness" after donation.
Secondly, post-donation rest and observation is of main importance. Majority of the Indian hospitals, the donors are asked to get up immediately, which does not allow the time for re-distribution of the blood properly and when the donor gets up immediately, there is syncope and resultant problems.
Thirdly, which is supposed to be the "most common" is psychological which happens commonly in "first time donors". Hence these people should be counselled in the pre-donation session so that they are totally relaxed during the procedure.
Fourth aspect is , if the donor donates on empty stomach, it happens. If the donor has "over eaten " also, dizziness or vomiting can follow, as post donation complication.
Fifth, if the donor is coming to the Blood bank completely drenched in rain, or if it is chilly weather , he should be asked to sit, relax, and given a warm cup of coffee, before proceeding.
Sixth, any donor, walking into the Blood bank for Blood Donation need to be honest in answering the "questionnaire" given to him and should be free of any sort of medications . If he/she is taking some medications, he should divulge the information to the Blood bank Director for him to decide on the eligibility .

Best wishes...

Some people just get queasy at the notion of giving blood, but the more common reason is that when you donate, you're giving one pint of blood. Your blood volume decreases (but only for a little while), which can make you feel dizzy/lightheaded. Your body makes up for the lost blood pretty quickly, so the feeling doesn't stay for long.

Blood carries oxygen to your cells and organs, etc. If you take it out of the body it takes a bit for your body to compensate therefore making someone feel a bit weak.

nothing but psychological symptoms

In normal cases it is more psychological than physical.

You're losing a pint of blood that your body is used to having. It's pretty common to get dizzy when you lose blood.

Purely psychological.

its natural. There is less blood going to your brain, so less oxygen, after lying down fro some time & taking some fruit juice with lots of sugar, you will feel alright.