Depends on when you took your previous courses, and who taught. My instructor was adamant that I learn some physics/physiology/etc during OW, Advanced and Rescue. I recently completed the IDC and IE and found that the theory is very similar to the DM course (however, I will admit the instructor admitted to drilling me more than required on the physics). The Diving Knowledge workbook was something that helped me a lot - I completed that several times and used that as a study guide and quick reference prior to taking the exams. Seriously though - for the IDC, study like you were in college. The IDC was unlike anything I'd EVER done before (and I have a masters degree) - it was incredibly intense, long days, hard work, and the more prepared you are in the theory the better off you'll be. You don't want to just memorize it - you want to UNDERSTAND it, and understand it well.
Congrats on your new journey - it'll be a wild ride but the sense of accomplishment afterwards is awesome.
Congrats on your new journey - it'll be a wild ride but the sense of accomplishment afterwards is awesome.