W8 completed - no drama, roll on W9!
I've found that the key for me is to keep it slow, especially to start off REALLY easy and very slow and get over the doubts of the first 5 - 10 minutes before even thinking about quickening the pace to slow! If I feel able, I might speed up slightly for the last minute or so, or I might save it for the next one.
If I feel that I'm tiring, I change down a gear, I don't know if this is technically correct - I shorten my strides - more than once if necessary - even if it means I'm only barely putting one foot in front of the other, I soon feel rested and can lengthen them again or increase the frequency. This is my technique for hills too, same as in the car - change down and increase revs (stride frequency).
Just thought I'd post this as it might help.
Like Jo keeps telling me - it's about keeping going to the end.
Wishing you all good running.