Been checked by cardiology, nothing wrong. yet after exercise at high hearthrate dizzy and unstable hearthrate for minutes.. what could cause thuis?

Fast heart rate: Have you had a monitor during the episodes? It is difficult to answer without documentation of the heart rate and rhythm during an episode of your symptoms.

Intensity?: You may be working at too high intensity.Also make sure your minerals are being replaced if sweating profusely with exercise. Try to cool down before stopping exercise.

Arrythmias : You should have an exercise stress test to evaluate your symptoms and electrocardiographic findings .