It is. I tested it with a shoelace and a spoon, was about to lose consciousness and would've died if I went through with it.
I felt little to no discomfort, it was way more comfortable than partial suspension and on the plus side you can do it while laying on your bed or wherever you want, you don't nedd to choose a place like with hanging to tie the rope.
Be careful with testing tho, if you are not fast enough at removing pressure there's the risk you could die by accident.