I got to that stage at about 20 miles yesterday suffering I thought with very tired hip-flexors and a bit of a lowering of my expectational horizon of the task in hand. The truth was, I was really hungry and needed more fuel than I had eaten after Day 1 and before to Day 2 of the event. Yes, I was tired after 50 miles, yes it was both muddy and hilly but the old adage of 'Mood is Food' as well as some Trance Music that got me thru.
This consisted of a complete pack of Bloks, 500ml of Go-Electrolye and a fistful of Sausages. And boy-oh-boy it worked, very quickly I got fired up and back on the task in hand. I really blasted the last few miles thanks to 'The Splash and Dash' feed.
Might be worth considering when you are feeling knackered in an ULTRA.
Special thanks to Ian Calder (very kind), Matt Hebden (very funny) and Neil Thubron (very accommodating) for a great weekend of friendship and fun.