How often do people switch careers?

This is a heavy question. I would suggest you lean towards some kind of engineering, because they can be used for a variety of similar fields. For example, a degree in electrical engineering will also help you transition to some IT-related fields.

This is a very great question with a lot of possible answers. I would recommend that you do your very best to find at least the general career area that you are most interested in. Nothing is worse than going into a particular field just because "it makes sense" and you have no real passion for it. You can take many free personality and career tests online that will help you get an idea of where your talents lie and what you would be good at. This is my favorite free one that tells you a lot of accurate info about you as a person and what types of careers you might excel in. http://www.typefinder.com/

Don't worry if you don't have a clear passion at this point in your life. It's completely normal to not know what you want to do with your life. It can be very scary to make a big decision like where to go to college and what to major in especially when it has such a large financial impact. Don't take this decision lightly. Be realistic but at the same time do what you love. Changing your mind and your major in college can be very expensive so do your best to figure it out the best you can. Best of luck!

People change their careers multiple times especially with the economy. It is okay to not have a clear cut idea of what you want to do. It is also okay to change your career path.
Think about and write down what your Skills, Talents, Abilities, and Goals are.
What type of environment do you like to work in? Do you like working with people, things, or data and ideas?
What are your favorite subjects in school? What do you enjoy doing? What do others say you are good at?
These are the types of questions you need to ask yourself to begin thinking about what you want to do.