What's happening here?

Yesterday I went for my usual Tuesday lunchtime swim. I soon realised I forgot my towel, but knew I could borrow my flatmates (who was swimming with me). That's not really important, though, as less then 1km into the swim, I started to hit the wall, or "bonk", as my mate put it. (I wish) What's this? 1km and bonking? I got out, borrowed a towel, and had something to eat as the others finished off their session.

Now this is not normal. I do not bonk after 1km. So why did it happen? Probably the huge amount of training I did on the weekend (7 and a half hours on Saturday), and the huge run on Monday morning (2 hours). I included intervals in each session, which also requires a huge amount of concentration and perserverance to continue. Which probably explains why I am also mentally frying.

I need a few easy days to get back to into the swimg of things, and I need tomentally recharge.

BTW: at climbing last nite I was severely lacking motivation. Luckily the company and food afterwards always makes for a good nite.