3000 + Calorie burn days. Food Intake??

Hi all,

I have a question about days that I have really high calorie burns. Im on a exercise routine hybrid of P90X and Insanity. Typicall on the Insanity days Ill burn around 1000 per hour as Im working out at 90%-95% of my max HR. Besides thse routines Im just natrually active. I like to be outdoors I find it mind clearing and relaxing. So today I will do my Insanity and burn about 800-900 calories and then will backpack (25lbs load) with a friend later on for an hour. This will put me around another 800 calories. Or later in the week I will be doing a 6hr backpack (25lbs) and that will put me around 4000 calories beside my BMR and daily exercise.

Obviously I cant eat back all of those calories. Maybe 2500 for the day. Do you think my metabolism will freak out if I have a 3500 deficit for a day? I just enjoy nature but am afraid Im going to screw up my metabolism by overtraining.

Any advise is appreciated!!