More than 40,000 runners will be feeling pretty sore today after completing the London Marathon on Sunday.
Elite runner Hayley Carruthers is already back at work despite crawling over the finish line.
“I started counting my steps and my head was gone, I think I lost sight in one eye,” Hayley tells Radio 1 Newsbeat.
“I just couldn’t lift my legs at all and I just couldn’t move.
“It was just petrifying.”
Hayley, who’s 26 and works in the NHS, says she started to feel bad just after the half-way point.
“My legs felt like lead and I felt sick.
“It gradually got worse and worse.”
TV viewers and spectators on The Mall watched as Hayley approached the finish line at 26.2 miles before her legs gave way – she fell just metres before the finish.
“To get to 20 miles and think I’ve still got another 10km to go – I genuinely didn’t think I could finish.
“It’s the hardest thing I’ve ever had to do.”
Despite crawling over the finishing line with the help of marathon marshals, Hayley still managed to beat her personal best time by three minutes.
She crossed the line in 18th place and says it was the toughest thing – physically and mentally – she’s ever had to do.
“We started too fast and I got carried away with the excitement of being in the elite race and all the excitement of London really.
“We ran the first half far too quickly and it just ended up being a survival fest.”
Hayley, who lives in Birmingham, says she’s learnt how hard she can push herself but also what happens if you don’t pace it right.
“To cross that finish line is a challenge, but it is doable.
“Now I’m going to allow my body time to adapt and go back in to training and make sure I don’t push too hard again too soon.
“You learn more from the races that don’t go as well as you’d hoped.”
Hayley is back in her day job as a cancer research radiographer today and says that because of post-race euphoria she’s not had much sleep.
“I’m running on caffeine at the moment.”