Unwanted experience

Bank holliday Monday, I had a nasty experience in the afternoon. It was 24c, but I was cold and shivering. I put a fleece on, and sat in the garden for half an hour to warm up. Got up, and my legs didn`t want to go anywhere. I used a walking frame to keep upright, and finally could walk by myself around ten in the evening.

I am a little concerned this may happen again, so being very careful. Maybe the answer is to keep warm, but time will tell.
Anyone had this unwanted experience?