I've gone back to running Wk3 as Wk4 has me defeated. Three times I tried to run Wk4 but I just couldn't do those final 3 minutes of the last 5min run. The last time I had to stop completely as I thought I was going to pass out.
I usually struggle for the first couple of runs in a new week but then my body gets used to it and I see improvement. It usually takes me 2 or 3 weeks to finally manage to complete the runs but I do it. There was no improvement in wk4. I just got worse and hated it more and more.
I've gone back to Wk3 to make sure I don't lose the fitness I've gained so far and have had no trouble. I've tried changing the time of day I run. If I jog any slower I'll be walking. Wk4 now looks like a looming barrier that I don't feel like I can face.