Being a fixed wing guy with instrument rating, transitioning to Rotary, I was doing my Solo flying for my PPL in an R22 flying up the East Coast to ST Abbs from Newcastle UK.
It was one of those clear winter afternoons smooth cold air and clear skies, when I saw one of those puffs of cloud over Berwick on Tweed which just looked like a ball of cotton wool hanging there.
It was only a little higher than I was flying do I decided to fly over the top of it. Big mistake - as soon as I couldn't see the ground under the bubble, but just this white cotton wool I got serious vertigo. Couldn't get away from the cloud quick enough, and have always stayed under the clouds when flying rotary ever since.