It seems like your present-time complicated feelings for someone are relevant to this dream.
In the dream, you’re back in high school. This is usually a discombobulating for most of us, especially when it comes to romance, so something about your present situation may have echoes or similarities to a situation during your high school years, or to the way you felt then.
The pharmacist (who dispenses medicine to make you better) is a figure for your higher self (or however you call that). She is calm, indicating that the situation isn’t as bad as you’re concerned about. Your ‘smaller’ self is wrapped up in the scenario and is having a hard time looking beyond the situation at hand.
The bus crashing into the water, as opposed to your usual car crashing dream, may mean someone else is at the wheel of the out-of-control vehicle and you’re sort of along for the ride. They assured you riding with them was safe and you trusted that, but it didn’t turn out to be true. This may have similarities to the situation with your relationship in present time. Have you sort of given control of your life, or parts of yourself, to this romantic interest, but you’re not comfortable with that?
It may harken back to a similar situation you had when you were younger, which is making you feel anxiety in present-time, similar to a time in your youth involving a rush of hormones, confusing relationships, mixed signals. It may be making you feel you’re not in control of your own life or self.
If you have a similar dream again, ask your pharmacist what you should do to stay healthy.