In March, you'll go to Everest Base Camp to study hypoxia. How did the project begin?
I was one of the team of people who came up with the idea for the original research project (conducted on Everest in 2007).
After I qualified, I spent a bit of time working at University College London Hospital in intensive care, which is unusual for a GP.
We're told that critically ill patients are hypoxic and therefore sick, so if we give them oxygen they'll get better. But that isn't true, and people die quite regularly in intensive care almost regardless of what you do to them.
We know from our experience of climbing mountains that when we reach altitude, we become hypoxic, and different people respond in different ways. That clearly echoed what we were seeing in intensive care.
So we thought there had to be some similarities, and we started Xtreme Everest.
My role this time around is taking one of the Sherpa treks. Colleagues from the previous trip and I will support and hopefully inspire the next generation, without stepping on their toes.
Dr Sundeep Dhillon testing equipment
When did you start climbing?
It's linked to the death of my parents. The day I started school when I was 13 my mother died unexpectedly. I went back to school, was there for three days and then dad died.
I was really in a lot of turmoil and then one of the teachers said: 'We're going away at Easter to go walking.' From a mental perspective, it freed me from just feeling sorry for myself to enjoy the hills and the mountains, and that aspect of it still holds true today.
At university, I started climbing serious mountains and I found that I didn't suffer from altitude as much as other people. So I set out to do something called the Seven Summits, which is to climb the highest mountain on each continent, and was lucky enough to break that record when I was 28 and hold it for four years.
How difficult was that?
In 1996, the year of the big storm, where lots of people died, I was on the north side of Everest with a fellow climber and we got to within 400m of the top. We realised that we might get to the top but we wouldn't come back.
It was horrendous. I was 400m from breaking a world record, I was straight out of medical school with debt, and I'd taken yet another three months out of my life in order to do this. And I could see it, but I couldn't get there. That's probably, with hindsight, quite a useful metaphor for life, but at the time it was absolutely heartbreaking. You do silly things like start crying, which then freezes so you feel even worse.
When we decided to turn back, it was about the time we were due an oxygen bottle change. Very soon after, we ran out of oxygen and crawled down in quite a bad way, only to find someone from an adjacent team had died. So when we got to the top camp we had to bury this guy and carry on down in the storm. It was one of the most horrendous experiences of my life.
What do you enjoy about climbing?
We can sit in a room and we judge people on how they look, how they sound, what they're wearing and what they tell you. You take someone into the mountains, you make the weather a bit interesting, add some hypoxia, sleeping on rocks and bad food, and suddenly the illusion of who you tell other people you are, or even who you believe you are, gets stripped away. The real person inside is revealed.
Contrast that with the stress of getting into work today and being a bit late, and you think about it and it's absolute nonsense. We fuel ourselves on false stresses.
How different is it, being a GP in the army?
I've always been based in the UK but you go overseas with your unit. For me, that's been Afghanistan lots of times, Iraq, the Balkans and the Congo.
As a military GP you live among your patients, you know all of them. They're as likely to ask you something in a dinner queue as they are to formally come and see you. That's both challenging and a privilege.
What will you do next?
There's probably another climbing trip to Everest in the not-too-distant future. Nepal for me is exciting for so many more reasons than big mountains. Apart from it being a mountain, it's exciting passing through the Sherpa community and meeting old friends and getting to know new ones. If you brought the mountains into your own cultural space, they'd just be lumps of rock.