I did it! With runs 1 and 2 being a disaster suddenly it clicked with run 3, I upped my water intake the day before as advised by the lovely people on here, my 2 litre Evian bottle was never far from my side, and slowed right down (I didn't think going slower was possible) and bingo, run completed without any dramas! I left the house this morning feeling very dispirited and came back feeling on top of the world, today I feel proud of myself!
Thank you all for your wise words of wisdom x