Lately, i've been experiencing dizziness and momentary blackouts from laughing really hard. what can be causing it?

You are: doing what is called a "VALSALVA" ( Like holding your breath and "straining down"...it causes a slowing of your pulse and drop in your blood pressure which can cause FAINTING !!!!!! If I'm correct being AWARE of this could possibly prevent it!! Hope this is helpful Dr Z

La k if oxygen or .: If you mouth hard you may be holding breath , lack of oxygen can make you dizzy. Other possibility is “ partial seizure” triggered by laugh. Whatever is situation if persists see your MD. Keep healthy life stifle ( avoid excess alcohol and sleep well . Avoid junk food . Get regular exercise . .

Syncope: We call blacking out syncope. There are several different causes of this. Some of these causes can be significant or serious so please see a doctor as soon as possible.

Vagal Response: Hard laughing, like coughing or retching can stimulate the VAGAL NERVE, an important nerve regulating our parasympathetic system. This nerve travels from our brain down to the pelvis can be stimulated through the movement of the diaphragm. Like brakes on a car, it slows heart, lowers blood pressure. Your brain gets a sudden change in blood flow and you feel dizzy. Not dangerous!

Laughing: Forceful and vigorous laughing can lower your blood pressure and slow down your heart rate by restricting blood flow to the heart from peripheral veins. Also, stimulation of the vagus nerve may play a role in your symptoms. I think the mechanism is similar to holding your breath and bearing down which can cause lightheadedness and loss of consciousness.