What exactly happens when you get toxic shock syndrome? i know the symptoms but what is happening in your body? how do tampons cause it?

Vascular collapse: Bacteria grow in the vagina around the tampon that has been left in place for a period of time. The "toxic" byproducts of that growth get into the bloodstream through the vagina and release pyrogens(fever agents) in turn those toxins act on the capillaries and arterial endotheliums(cell walls) to turn them into "sieves" causing extravasation of the blood contained in the vessels and "shock".