Has happened to me. Fairly serious condition by the look of it. Took at least 30 minutes to get the pax off, during which they stabilized and hooked up drips etc. Annoying part of the experience for me was a missed connection as a result of the delay - The plane was already late on an international inbound leg connecting to a domestic. Nothing I could do but watch, it was a seat 2 rows forward and on the other side of the aisle from me.