The biggest issue would be muscle atrophy. Even if you're pretty sedentary, your muscles are doing a lot of work each day just to move you around. Being bedridden for even a few days can cause muscle loss. You also increase the risk of blood clots and bed sores.

Medically induced comas also come with risk of permanent injury or death, so they really only do them in absolute emergencies.

And lastly, there are already surgeries and medications for weight loss that work much faster. The issue is, without matching lifestyle changes, all that weight will just come back.