To me it sounds like something to do with anxiety. From what you're saying, the feeling you're getting is similar to when you're on a roller coaster and your stomach drops? The thing is, anxiety is caused by, you could say, too much adrenaline. When the brain senses danger, it gives us adrenaline. Your brain is just seeing danger to the smallest of things that are not dangerous at all - your brain is basically working overtime!
In a safe place, try closing your eyes and focusing your breathing, really deep breaths in and out. However this exercise is temporary - when you feel that 'drop', use it, it will help! Long-term I would talk to a doctor or even better, a psychologist about what you're feeling.
Don't worry we're here for you, you aren't alone, ever! :))