I spent half that time in Critical Care (much of that on a ventilator, a small amount sedated), and most of the rest in a specialist neuro-rehab unit. I would have died otherwise.
Fortunately it cost me nothing - Thank Bevan for the NHS - but if I were in the US I imagine I would be financially crippled!
In the U.S. with insurance you would have easily hit the deductible and out-of-pocket costs though that does mean you would have been billed a few thousand dollars easily (on top of the regular monthly insurance costs). Everyone has slightly different health insurance plans so the actual amount would be hard to predict for a hypothetical question.
One thing you got me thinking, I’m not too sure how often U.S. insurers would actually cover someone to literally stay 4 months in a hospital, maybe in rare extreme cases? Insurance companies typically only approve x amount of days/weeks in hospitals or rehabilitation facilities so once you use up those approved days the hospital has to figure out how to get you out or start billing you directly at a few thousand per day.