It is not horrendous at all.
It actually kind of felt good. The body begins to feel weird like everything is turning into jelly is the best I can describe it. It is lights out after that.
No feeling of suffocation and no pain, and definitely no panicky feeling because of the nature of what this drug does to block adrenaline. No need to use an antianxiety med.. unless you wanted to for some reason.
It is peacefulness at its finest when it comes to suicide by way of an overdose using pills, in my opinion.
I think the immediate release version will turn the lights off to cause unconsciousness in practically no time flat for most people, like within 15 or maybe 20-30 minutes max after consuming all of the drug.
8-10 hours needs to be allotted as the timeframe to death, or else you could be rescued prior to your dying. If after being rescued and if you are very lucky (lucky as in chance) you could be successfully revived over the course of many hours, then days in the ICU, and possibly weeks being spent in a hospital. And then likely some time in an inpatient psych ward for a few weeks to a month or more after all that is over, for a near full recovery of your health. . . . if you are very lucky.
If things do not work favorably for your recovery, you may have just become a vegetable. Or, severely cognitively challenged, maybe a stroke, maybe a heart attack and/or heart failure, maybe you now will need dialysis for life.. the maybe list is a long one for the possible sequela which could result from a failed attempt when using propranolol.