Laughter on a ward is a real phenomenon and it is almost never about anything funny. Two people in adjacent beds will find something helpless and absurd in a gown that doesn't close, or in the fourteenth person to ask for a date of birth, and be gone for a full minute.
Nobody outside the room would understand it. It isn't bravery and it isn't denial. It is a body insisting on one of its own functions in a place organised entirely around what is failing.