In short, Hillary was telling Michelle what events she wanted her to go to. Michelle put peg to that, but in the process Hillary got into a coughing fit. When it did not end within a short period of time, Obama got one of his own doctors on call to come in to help her.
Both Obama and Michelle left the room while the doctor treated her, He came out several minutes later telling Obama she was okay.
Later Michelle speaking with others said that there is no way the Hillary they saw that day can function without some sort of medication.