Was I tired? Yes!
Obviously this indicates that I still have a long way to go. My training plan (previously posted) shows this anyway. So whilst it was slightly worrying just how tired I was (bearing in mind I'd have to do all of that another four times and more), I have time on my side and a plan in place.
What's more, the pool yesterday was warm. VERY warm. It's fantastic to have access to the training facilities, and as yet it is still too cold to swim very far in unheated outdoor pools. But 8km (5 miles) in that heat, with a head of hair that I'm still getting used to, was draining. All I wanted to do when I exited the water was jump into a cold shower and cool down. In fact, I was hot for the rest of the day!
Only time will tell if I find such a distance equally as draining in cold water. In the mean time, a mixture of distance, anaerobic and aerobic training continues in earnest.