People climbing Snowdon are being urged to wear appropriate clothing after a man who reached the summit in just his pants developed hypothermia.
Nathan French, 19, took to the highest peak in England and Wales in his Superman underwear to raise money for charity.
But a paramedic was called to meet the Liverpool student after his descent.
Phil Benbow, of North Wales Mountain Rescue Association, said they were seeing more unprepared visitors.
Mr French, of Halewood, Merseyside, decided to take on the challenge to raise money for a dementia charity after his grandmother developed the condition.
He said he became unwell at the summit after completing the 1,085m (3,559ft) climb on 9 September and returned to the bottom on the Snowdon Mountain Railway.
"I keep fit and I am healthy but I was taken by surprise by how cold I got," he said.
"I was shaking uncontrollably and they covered me in tin foil.
"On the train down I started to feel really sick and I started going deaf and my eyesight started going funny. I started getting really emotional so my dad, who was with me, decided to call an ambulance.
"The paramedic who met me checked me over and said I was showing early signs of hypothermia."
The Welsh Ambulance Service confirmed it responded to the call.
"We sent a paramedic in a rapid response vehicle and a first responder and a man was checked over at the scene, but did not require hospital treatment," a spokesman added.
Mr Benbow, who also volunteers with Llanberis Mountain Rescue - the team that covers Snowdon - said while it was "laudable" to undertake charity treks up Snowdon, it was essential that people dressed appropriately for the conditions, planned their trip and checked the weather forecast.
"We have a significant number of calls every year about people on Snowdon who are not equipped properly," he said.
"They make an assumption that because there's a cafe at the top and a train, that it's a walk in the park. It's not - it is the highest mountain in England and Wales and people need to respect that.
"Our team has been called to 173 rescues so far this year and that will be over 200 by the end of the year - the third year in a row we will have topped 200.
"That's way too many for our volunteers who have to give up time with their family or at work. People just need to think ahead."