Being stressed and fatigued is the emotion that affects most peoples abilities to drive in a safe manner as being stressed out can cause you to lose sleep, become angry and upset and can lead to distraction while driving.
If you're very stressed you should really avoid driving if possible until the stress goes away or you can get the stress under control.
Being stressed out doesn't only affect your ability to drive it also affects your health by raising your blood pressure which can lead to heart disease and heart attacks.