My onset was incredibly sudden. Seconds, not minutes.
I was crossing a road, in the middle of a very enjoyable long walk of several miles. (I was very fit.)
On one side of the road I was well, by the time I reached the other side, I was wading through a lake of treacle.
11 years on, I'm still trying to wade through that lake of treacle.
A few weeks beforehand I'd been with family for the yuletide season. My brother's partner had 'flu. I caught a sniffle from him and so did my brother and my partner.
My brother's partner came down with ME at the same time as I did, my brother got a 9-month PVFS, my partner got IBS.