Photo: Shanda Hill Ultra Athlete

Imagine completing 20 back-to-back Ironman triathlons ... taking a few days off – and then doing it all again.

That's what Vernon ultra athlete Shanda Hill is doing right now, in San Felipe, Mexico.

Hill completed the gruelling Swiss Ultra Triathlon only 10 days ago, but over the weekend she dove into the swim at the Decaultratri Mexico Double Deca Continuous.

Hill is currently nearing the end of the 76-kilometre swim, which will be followed by another 3,600-km bike ride, and 844-km run.

And this time, she's doing it under the blazing Mexican sun.

Hill battled some seasickness in the pool and, due to the heat, swam without a wetsuit, leading her to take a break Sunday to avoid sunburn before resuming her swim at night.

This time, at least, she's swimming in a pool filled with spring water, so she won't suffer any effects from prolonged chlorine exposure.

But, sleep deprived and running on fumes, Hill fought hallucinations throughout the night Saturday.

At one point, she thought the pool had morphed into a twisty maze, and she had moments when she imagined snakes on the pool floor, her support team says.

After 26 days of almost non-stop racing in Switzerland, the Mexican double deca will be Hill's second this year and her third after becoming the first Canadian – male or female – to conquer the Mexican race in 2019.

"Completing this incredible feat will make her the first human on the planet to complete three double decas. Furthermore, she'll set a record for the most long-distance triathlons completed in a single year," her team says.

As well as travelling for 24 hours to get to San Felipe, Hill must also deal with the elevation change, going from 1,500 feet above sea level in Switzerland to 6,800 feet where she's racing in Mexico.