Both Prazosin and Clonidine have fairly short half-lives, so they won’t effect you the next day unless you take another dose.
Common side effects that occur immediately are sleepiness and dizziness.
This is exactly what you want if you’re in a life-threatening situation.
But prolonged exposure to those same stress chemicals is harmful to your physical and mental health.
These medications work well to increase sleep and prevent nightmares in people suffering from PTSD.