It's fairly common when the body is under either physical or mental stress. It affects the Qi near the outside of the body which affects the skin and circulatory system.

It can be seen in the iris of the eye. A dark ring appears around the outside of the iris which appears when the body is under either physical or emotional stress and affects the skin function first of all and the circulatory system the more stress on the body. It does tend to cause lowering of the blood pressure.

Anything which reverse that, favor warming foods rather than cooling foods, maybe some warm spices such as cinnamon, ginger and small amounts of cayenne might be helpful but don't overdo these! Veg tend to be cooling and apart from the fibre is probably best kept to a minimum. Warming foods should help normalize blood pressure and increase blood circulation and encourage the kidneys to filter the blood. Make sure that plenty of "clean" water is drunk. That should keep the bowel hydrated, the water volume in the blood sufficient and should help to maintain the blood pressure to some degree.

Yes it can be caused by toxins in the blood, breakdown of yeast/fungi/bacteria which release their toxins could have this effect.

Use anything which helps the body to detox and retain toxins in the bowel using soluble fibre, rather than being absorbed into the blood stream. Keep the bowel moving!