C S Miller writes: Not much more to add.
The BBC is reporting that "Stephen Hawking is 'very ill' in hospital". He has had a few health scares before, and as a post-graduate he was told he didn't have much longer to live; he's now 67.
I've never been canoeing before, but I imagine there must be just a few
simple heuristics you have to remember...
Yes, don't fall out, and don't hit rocks.