When Bubble Lee was filly, she and few of her friend tried scaling down a cliff to explore the sea caves down below in order to get their cutie marks for “Treasure Hunters”. Halfway down Bubble accidentally slipped, bumped her head on a rock and fell in the ocean, taking under by the strong current. A couple days later she was found on shore, with no memory of who she was or what had happen to her, likely caused by a mixture of the head wound and traumatic experience.
Every now and again, she gets vivid flashbacks: Sleep paralysis, lack of breath, the sensation of falling into an endless void. Drowning.
After waking up, she usually spend the rest of the night by the ocean, watching the tide come in, talking to the fishes, and lost in her own thoughts.