3 years, one major or 4 years, two majors?

Hi, everyone. I came into college with a lot of AP credits, and could theoretically graduate with a BS in neurobiology in a year. This would be a total of 3 years of undergrad. If I did this, I would go abroad (to Europe) for one year before applying to med school; I've always wanted to travel. My other option involves staying an additional year (4 years total) to get a second major in a subject that I am passionate about, psychology. I would be able to spread my hard science courses out more, so as to not overwhelm myself.

Currently, I am leaning towards the 3 year route, but my thinking has not been the clearest lately. I am bipolar, and a tad bit hypomanic, so every idea that I have now seems like the greatest idea ever.

I understand that I will likely become depressed in the near future, and when I am depressed, I lose my interest in travel. I want/need to be close to home to cope. So, I'm not sure that going abroad for a year would be the smartest thing that I could do. Yet, this is something that I really want to do.

I understand that the ultimate decision is mine, but which path seems to make the most sense to you?