MY eyelids feel heavy as every part of my body is engulfed in my warm blanket.
I feel more relaxed than I have all week, and I could fall asleep at any moment.
I know it sounds like I'm in bed, but I'm actually in a gym class burning 17 calories a minute - without even trying.
It's called the world's easiest workout for a reason.
Instead of star jumps, burpees and trying to lift weights I can barely carry, the class involves 15 minutes of easy stretching followed by half an hour horizontal in something called a sauna blanket - bliss!
It sounds easy, and it really is, but it still pushes your heart rate up to 150 beats per minute (bpm) - about the same as a light jog.
And attendees can burn as many as 500 to 600 calories in a single session - similar to a spin class.
The blankets, which are more like sleeping bags, reach temperatures of 70C.
As someone who hates saunas and steam rooms (which usually sit between 65C to 90C, and at 50C respectively), I was apprehensive about the idea of heat therapy.
But I was pleased to learn that while almost all of your body is enclosed, your head remains poking out of the top.
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It means not gasping for breath or having sore eyes like you might get during other hot spa treatments.
If that wasn't enough, sauna blankets allegedly aid weight loss, improve heart health, boost circulation, lower blood pressure, reduce stress, relieve aches and pains, and help you sleep.
Tempted? Here's everything you need to know.
What is the 'world's easiest workout'?
As the name suggests, the class doesn't involve doing much.
It focuses heavily on relaxation and meditation - but that doesn't mean you won't break a sweat.
When I walked into the studio, the Higher Dose sauna blankets were laid out across the floor.
I picked my weapon of choice, and was advised to keep my jumper and socks on to maximise the heat benefits.
The class began with some simple stretches, like downward dog and pigeon.
I then stepped into my blanket liner (a towel shaped like a sleeping bag) before shimmying into the blanket itself with my arms by my sides.
It turns out there is power in doing nothing.
Chlöe Warner
The instructor helped me ensure my shoulders were strapped in correctly, and my head was comfortably resting on my pillow.
Then, it was 30 minutes of breathwork, body scanning and meditation-based exercises.
Some of this was as simple as breathing in for four seconds and out for six, while other sections involved squeezing and releasing different muscles.
At the beginning of the 50-minute class, the sauna blankets were set to about 40C.
But the heat rose four times throughout, finishing at a maximum temperature of 70C.
"This stage is all about mentally overcoming the intense heat and releasing everything in the class," Chlöe Warner, personal trainer and studio creative at Gymbox, said.
"It turns out there is power in doing nothing."
Is it really that easy?
To be honest, I don't think you can really even call it a workout.
Yes, it takes place in a gym and an instructor leads the class.
But really, it's more like guided meditation while wrapped in a warm blanket.
And it's not even that hot. 70C sounds brutal, but it's basically a more intense version of an electric blanket you might put on your bed.
If anything, it was incredibly relaxing - I almost fell asleep! And I definitely wasn't dripping in sweat - I just had a light sheen.
The benefits
Scientists have been banging on about for years.
show it can potentially burn fat, improve circulation, accelerate muscle recovery, reduce pain and even help treat depression.
There is limited evidence about sauna blankets specifically, but some , and Gymbox, reckon it is hugely beneficial for the heart, circulation, weight loss, stress, aches and sleep.
Chlöe said: "With regular use, sauna blankets offer multiple benefits, such as improved cardiac health through temporarily raising heart rate, improved circulation, lowered blood pressure, reduced stress, reduced aches and pains, accelerated muscle recovery post-workout, improved sleep and improved skin condition."
Lying in a sauna blanket can allegedly push your heart rate from its baseline (of about 73bpm for a 30-year-old man) up to 150bpm, which is similar to a brisk walk, climbing stairs or a light jog.
The target heart rate zone for a man in his 30s to burn fat during light to moderate exercise is 95 to 162bpm.
Thirty minutes in a sauna blanket can also burn between 400 and 600 calories - about the same as a 60-minute spin or circuits class.
Unfortunately, you can't wear any jewellery or a smart watch while inside the blanket, so I can't know exactly what my heart rate reached or how many calories I burnt.
But someone of "average fitness" reportedly sweats 1lb during a class.
"While it may be minimum energy, it has maximum impact," Chlöe said.
So it's really no wonder why celebs like Maya Jama, Selena Gomez, Kim Kardashian, Zac Efron, Gwyneth Paltrow, and Lady Gaga have previously praised the technology - though it seems they haven't all tried it in blanket form, yet.
Infrared saunas are also available in the more traditional form of a room with wooden benches.
The old school ones warm the area around, but a blanket uses infrared to directly warm the body itself.
My verdict
After just one session, I can't say I noticed any real results - other than I felt chilled out and very sleepy!
But I can see that after repeated sessions, you might start to feel even more relaxed long-term, and flexible.
It's definitely not something I would replace my usual workouts - dance, spin, strength and HIIT classes, plus running and swimming - with, but I can see it working to supplement them.
And I did that post-workout glow - although it could have just been my rosy cheeks burning from the heat!
It's also great for people (like me) who can't stand actual saunas or steam rooms, which can be incredibly stuffy and sometimes painful for the eyes and lungs.
How to have a go yourself
Classes are available at London's in Ealing (Mondays at 1pm), Victoria (Mondays at 7.30pm), and Elephant and Castle (Thursdays at 1.15pm).
They are free for members. Day passes are available for non-members for £20.
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Sauna blankets are not recommended for anyone with the following medical conditions, unless cleared by a doctor:
- Skin diseases, burns or reddening
- Splanchnic diseases
- Heart defibrillator or other implantable devices
- Heart disease or illness
- Broken bones
- Malignancy
- Nausea, headache
- Recent surgery
- Osteoporosis
- Abnormal blood pressure
- Pregnancy or breast feeding
- Anhidrosis
- Cancer
- Metal or other body implants, including breast implants