I've passed out from taking around 80mg of propranolol when I already had low blood pressure.
Your mileage may vary with medications if you've never taken them before. One person's sleepy dose may be like a placebo to someone else if the drug is metabolized differently.
But 800 mg is a very large amount, would be considered an OD. I have worried myself about taking such a copious amount of it, because of the risk of bad side effects and sleeping.