E! News has learned exclusively that the 49-year-old star's evening started off normal enough, with Moore hosting a birthday dinner party for a friend.
A source says that shortly after 7 p.m., a small group of girlfriends drove onto Moore's gated compound in the Beverly Hills area for the shindig in honor of the actress' good friend Heather Parry, a former MTV executive.
"It was just a party for a few girlfriends, not a big rager," the source insists. "No guys. Just girls."
Also among those at the get-together was Tobey Maguire's wife, Jennifer Meyer, a longtime Moore pal.
A source says Moore was "pretty hyper" for most of the night and was not her normal self, while another source adds she was "acting crazy."
And while Moore was seen drinking from a wine glass, the source didn't know exactly what it contained. The actress apparently left the party several times, only to come back minutes later.
Following dessert, the affair began to wind down shortly after 10 p.m. All the women began to leave, but one stayed behind.
This is where the details grow fairly sketchy.
A source says Moore, for unknown reasons, began to convulse and act "like she was having a seizure." The female friend was understandably concerned and dialed 911, prompting the LAFD to dispatch a team of paramedics, who subsequently rushed Moore to a nearby hospital.