Natasha Richardson, 45 Years Old
The "Parent Trap" star was on a ski vacation with her son at the time of her death. She hit her head while on a run, but seemingly felt fine after she got up. Sadly, she'd suffered from an unchecked brain bleed, and it killed her. She was married to actor Liam Neeson at the time, and he's spoken openly about how difficult it was to cope with her sudden death.