When i do the valsalva manoeuvre, my severe lightheadedness improves a lot. i think it also helps with my palpitations. why is this?

Valsalva: When you valsalva, you increase intra-abdominal pressure, reduce venous return, reduce the ventricular chamber dimension, reduce cardiac output, reduce blood pressure and stimulate the vagus nerve which slows heart rate. Net effect: it can help certain tachyarrhythmias. I would have expected it to exacerbate your lightheadedness unless that symptom is independent of your BP.