I ran down to work (5.8km), had an hour long meeting then tried to run home
Okay.
I forgot that I've not run once in the last nine months so now my legs are completely fucked
That's why. You can't go from not running at all, to doing 10 kms and expect to walk away without any issues. Your body has adapted to cycling so introducing running needs to be done gradually.
When I did this (I raced a 6 km corporate challenge thing with no running training whatsoever) I could barely walk the day after. The thing that helped me best to recover was a gentle spin on the bike.
Okay.
That's why. You can't go from not running at all, to doing 10 kms and expect to walk away without any issues. Your body has adapted to cycling so introducing running needs to be done gradually.
When I did this (I raced a 6 km corporate challenge thing with no running training whatsoever) I could barely walk the day after. The thing that helped me best to recover was a gentle spin on the bike.