What could be the cause of dizziness and shortness of breath and loss of memory after running?

Multiple things. Dehydration can lead to SVT and other fast arrhythmias. Shortness of breath could be due to simple fatigue, anemia, possible pulmonary emboli if it is abrupt onset, also, electrolyte imbalances play a key role in how you feel. Drinking to much water too quick after running cause massive shifts in electrolytes leading to dizziness, heart arrhythmias and worst case scenario, encephaloathy of the brain and death.