Well I dont know what went wrong there. All other runs have been fine and achieved. Wednesday evening went out and as soon as I started jogging my knees felt too heavy-dont think Ive put on a couple of stone in the last couple of days either! Had trouble getting into a comfy pace for about 3 minutes, but then ok. Dont feel very confident about what i did, but I did complete the 2 8 minutes. Decided to have 2 days off before the 20 minutes, dreading it at the moment if my knees to the same thing, but have to go with Lauras advice. Mentally I may be wary, but have managed it all so far, so its got to be working!