Moved to runs with no walking times last week and really struggled with 20 minutes. Was knackered after 5 minutes and when I tried then and even on shorter runs could not slow down. I watched a video posted on here about foot strike and it lead me to a guide for early runners. On there it said that you must try to keep the same tempo but increase or decrease your stride, so shorten uphill or if going to fast and lengthen downhill or to speed up. Went out today for 25 minute run and found it fine, even managed a sprint at the end prompted by naughty Laura. My time per km had increased by 30 secs, but it is not a race is it.
I am sure that I was trying to slow down by reducing my tempo and losing all the rhythm in my running, it just did not work. So, Oldfloss your advice, about slowly does it, was no where near as easy as it sounds. For me anyway.