Interior design is a 'registered' body, you must have completed interior design education in order to be part of of the ASID/ARIDO etc.
OTHERWISE you cannot, by law, call yourself an "Interior Designer" (you can call yourself a interior decorator, or space planner, or whatever)
Industrial Design on the other hand is different, ANYONE can call themselves an 'industrial designer', from graphic designers who once sketched out a chair, to interior designers who spec'd a custom cupboard pull. (we as ID'ers are not an accredited body, unless we want to call ourselves "registered" industrial designers)
So if you like working and if you like flexibility, interior design might not be such a bad idea , since you can still call yourself an industrial designer.
Plus you will have access to not only Interior design companies, but also furniture companies, architect offices, engineering offices, marketing offices, exhibit firms (basically everywhere since you can always be brought in for "space planning" and layout.)
I unfortunately cannot say the same accessibility to various jobs exists for industrial designers. (that is without begging and convincing them that an industrial designer "wtf is an ID'er" can be a useful and productive member of their team)
Good luck on your decision. in the end it is a follow your heart type of thing, but keep in mind you should know what it is in design that you actually like.
is it the creativity, is it the black turtlenecks and percieved 'hipness', is it this cool core77 site and others like it?
I really would suggest to try imaging what the day to day ins and outs of the profession are like, and seeing if design still appeals to you. designing telephones, shoes, watches, aeron chairs... even the coolest products gets tiring after the first few years. especially when young punks just starting in the I.T dept make more $$ than you do with more than 5years experience. I won't even get into how the design dept will be the first to get 'trimmed' when times get tough, you'll be long gone before anyone in HR, marketing, accounting etc even have to start worrying about being 'called to the office'.
(Note to Canadians and non-americans, you can join the IDSA even if you graduated from a one year "technology of design" course, since the IDSA seems to be granting professional membership to ANYONE, even if they graduated from a non accredited school....basically there are no non-American schools accredited with IDSA, why would there be since they are an American body, but they'll take your money and grant you professional menbership)