Same way you wake up dead.

Seriously though, one of the consistent things said by people who attempted to commit suicide by jumping from the Golden Gate bridge but survived were (paraphrasing) "At that moment, I realized that of all the problems in my life, this(jumping) was the only one I couldn't fix".

At that point, when it was too late, they regretted it.

There's a general consensus of immediate regret.

https://abc7news.com/society/second-chances-i-survived-jumpi...

Kirkegaard's existentialism was religious in nature, in contrast to the later atheist existentialism of Sartre. So it's quite possible that from Kirkegaard's perspective, it could be possible to regret things after your death (or maybe it's just a joke - I haven't read Either/Or, so I'm not sure how far along toward his religious phase he was when he wrote it)

I took it as a joke. It's a very silly and funny book, in parts.

There is a opportunity for regret in the short moments after kicking the stool away.

By failing to do so successfully, or by being saved before the damage is irreversible.