My involvement with Comic Relief over the past 10 years has always been in a comedic capacity, but I'd always wanted to visit one of the regions where they spend the money that's raised. I was asked if I'd like to join a group of celebrities trekking 107 kilometres across the Kaisut Desert in Kenya to raise awareness of the urgent eye care needed there and the millions of Africans who are at risk of losing their sight because of preventable and treatable conditions.
I wasn't without reservations: I'm not renowned for tolerating heat very well. I once got severe sunstroke in Ayrshire, Scotland, which didn't bode well for the 48C desert heat.
Before we set off, we were given a terrifying talk about the snakes, spiders and scorpions we would meet. They told us helpful things such as how long it would take for us to die if we were bitten by them.
For the first two days, we were on rocky, mountainous terrain, which made walking very difficult, but the vegetation and rocks provided some shade and there was a little bit of breeze. As we got into the true desert, the shade vanished and the heat went up considerably. It was really oppressive; a bit like having a dozen hairdryers blasting on you at all times.
The group, which included Dermot O'Leary, Lorraine Kelly and Kara Tointon, got on marvellously and we bonded incredibly quickly, which you tend to do after having a constant stream of lavatory conversations: namely when, how and where to go. It didn't help that many of the group were struck down by stomach bugs.
At the end of each day, we would fall into camp exhausted and absolutely filthy (apart from Craig David, who managed to stay meticulously clean throughout). We must have looked a state; the definition of a power shower was an upside-down can which emitted two drops of water at a time as opposed to one. I honestly had the local tribespeople, the Rendille people, coming up to me, fascinated by the wool-like texture of my hair.
I was one of the lucky few who didn't develop blisters, which was a huge advantage, because others suffered really badly. The whole experience was very tough but I was pleased with my resilience, which I put down to my peasant stock: I obviously come from a long line of potato pickers.
Along the way we went into villages with people from the charity Sightsavers and identified those who had extremely bad sight problems. We told them about the pop-up sight clinic at the end of the trek where everyone could get treated. Those in the area have appalling risks of blindness, mainly from trachoma and cataracts. With the money raised they hope to open up several permanent Sightsavers hospitals.
When we finished after five days and 107 kilometres, it was total euphoria. A group of schoolchildren sang for us as we came in together and it was very emotional. Word had got out about the clinic and seeing the throngs of people being treated by doctors and nurses was just fantastic. Some of these people are extremely reticent and nervous to go and see anybody about their concerns so it was brilliant that so many were there.
After things like this you often plan to meet up with the other people who take part, but it rarely happens. This was different. We saw some things and did some things that were very special. In fact, we're all getting together tonight to watch the documentary. With my hair brushed, they might not even recognise me.
The Big Red Nose Desert Trek will be shown tonight at 9pm on BBC1.
You can sponsor Ronni and the rest of the team of Comic Relief trekkers at www.rednoseday.com/trek.