(CNN)"Imagine the most exciting thing you've done in your life -- and then add that to the scariest thing you've ever done. That's what it feels like."
BASE jumping: 'The thrill, the fear and the excitement'
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Daniel Witchalls struggles to explain what makes him do it -- what persuades him to take a leap from the top of a skyscraper or cliff, knowing it could be his last moment on earth.
As a BASE jumping world champion, the Englishman has made more than 1,500 jumps from all types of buildings and structures.
BASE -- which stands for building, antenna, span and Earth -- allows athletes to leap from fixed points such as towers, mountains or bridges.
"There's nothing like it," Witchalls told CNN. "It's difficult to explain because if you think about it logically, it's ridiculous.
"You jump off something low, sometimes at night, with a parachute and you've only got one chance or you could end up smashing yourself or dying.
"It's the thrill, the fear, the excitement. It's something you can't explain unless you have experienced it yourself."
On Sunday, extreme sports star Dean Potter was one of two men found dead in Yosemite National Park, after attempting a jump from Taft point, authorities said.
Potter, who was well known for his daring exploits, had attempted to descend from around 3,500 feet along with Graham Hunt.
Both men's bodies were found during a helicopter search around noon Sunday, according to Scott Gediman, a spokesman for the park.
According to the magazine Outside, Potter and Hunt were attempting a wingsuit flight.
Potter, 43, is well known for his climbing and tightrope walking as well as the escapades of his dog, Whisper, who would often sit in his backpack during each daring act.
Such acts can produce chemicals akin to morphine and provide a high which enhances mood and can act as a pain reliever -- the more dangerous the jump, the more powerful the high.
"What is bizarre is that fear is essential to our survival as it keeps us out of danger, yet we are drawn to meeting it head on," says Professor Rhonda Cohen, an expert in the psychology of extreme sports at Britain's Middlesex University and head of the London Sport Institute.
"When you engage in extreme sport there is a feeling of stress in experiencing something scary as our brain is alerted to danger through different sensations such as screaming, sweating, heart pounding," she told CNN.
"We're frightened, yet we're also excited at the same time. At this time, we release dopamine which provides us with a pleasurable feeling.
"So we have fright and excitement together. Stress and fear along with euphoria means that even after you've finished, you want to do it again."
It is the buzz which has persuaded Witchalls to continue his career at the top of BASE jumping, to the concern of his family.
Witchalls, who is 39 and married with two children, has left the house in the middle of the night to go jumping despite the protests of his loved ones.
His parents have urged him to give it up while his wife, a skydiving enthusiast, is looking forward to his retirement.
"It's the people who are left behind which suffer," says Witchalls. "For the individual, they know the risks and what's all involved.
"I've got a wife, two young kids, and my parents have been on at me to give it up for ages.
"I will give up eventually -- it's just about knowing when the right time is."
One of those who decided to give up BASE jumping is Tim Emmett, who shared many experiences with Potter.
Emmett, an Englishman now living in Canada, took the decision to retire two years ago after experiencing a couple of close calls and losing his friend Sean Leary, who passed away after being involved in a wingsuit accident.
But Emmett, who began rock climbing at the age of 15, says the lure of the wingsuit remains real -- each trip to the mountains makes him ponder the feeling of flight.
"Wingsuit flying is an experience like no other," Emmett told CNN. "You are flying your body and you're in control of which way you go.
"It's an incredible feeling -- it's unlike anything else I've ever done.
"When you're flying, the focus you have is more tuned than any other situation you've ever been in."
While Emmett now sticks to rock climbing, the new generation of BASE jumpers have already helped the sport grow.
The use of social media has meant millions can watch online just seconds after jumpers have landed on the ground.
A quick glance on Facebook or YouTube will show that there are hundreds of videos showcasing the latest jumps from across the world.
"For some people it's a part of their personality as they enjoy the thrill of the experience," says Cohen.
"It may provide a relief from the scheduled structure of everyday life -- there's a sense of achievement.
"Doing something which pushes you beyond your usual boundaries also provides you with a great sense of accomplishment and a real sense of pride."