In some people with dysautonomia the brain does not get these messages correctly and their blood stays in the lower part of their body and then their blood pressure drops and their heart rate increases. This can cause them to get dizzy or faint and other symptoms may happen. It is something like going into shock. Also, because these people don't always get enough blood to their brain they sometimes have times when they don't think very clearly and can't remember things very well.

They can be highly intelligent people who briefly forget things like their best friend's name or the word they were just trying to say. Low blood pressure does not impact their intelligence, but it impacts their ability to think clearly and to concentrate. This impact on concentration is usually brief and comes and goes according to the amount of blood getting to the brain. Sometimes people with dysautonomia feel fine and have few symptoms; sometimes they just feel slightly dizzy and "foggy" and can pretty much go about life normally, but sometimes they have so many symptoms that they have to lay down all the time. The reason their heart rate often goes very high is that their system is automatically responding to the drop in blood pressure and attempting to pull up the blood pressure by increasing the heart rate. This can be the cause for a lot of tiredness and fatigue and generally feeling washed out.