Jeremy, I agree with cym's advice above -- 1,800 calories is just too little for a guy your size. I would start with a diet around 2,750 calories. As cym says, that will still give you a nice daily deficit.
Also, I would NOT do HIIT or high intensity cardio until you're sure that your ticker is OK. At your weight, you don't want to take chances with pushing your heart too hard. If your doc gives you the OK, start off slowly. Do some 3 or 4 minute intervals at 70% or 75% of max. As you get used to that, build it up from there.
I did interval training for 3 months before I even tried HIIT. Now I can do sprints and hill climbs with the best of them, but I got there gradually.