The 70-year-old singer revealed that watching his parents and in-laws suffer drawn out deaths made him realise he wants to control how he passes away.
His decision was strengthened when he recalled a terrifying plane journey from Paris, France to Stockholm, Sweden when one of the engines shut down and he was thought he was about to die.
Ulvaeus tells Britain's Daily Mirror newspaper, "It is my life. It's the thought of the endless pain and suffering that I am afraid of. This should not be necessary. I have seen this misery up close. My parents lived long but would have preferred a more painless and dignified ending. The same goes for the parents of my wife. My mother-in-law has lived for a long time but she could not express her feelings.
"That was where I thought, 'I don't want this'. It is my life. Why can't I control how it should end? I understand this might be controversial, doctors want to lengthen lives, not end them. Patients might want to change their mind at the last moment and are unable to articulate this. But whatever it is, it is my decision.
"(When I was on the flight) I tried to remind myself that the plane could easily land with only one engine - but I got a full-on panic attack. Later, I realised the fear stemmed from the fact that I had no control over my own death. That was a scary realisation. Now I've begun to think, 'Maybe I will not see many more summers'."