Exercising on Pre-Op

I'm on day 5 of my pre-op diet which consists of 800 calorie / 1200 calorie blended diet rotation. Protein intake is 28-56 grams a day. 3 meals and 3 glasses of skim milk for my Snacks.

I've been feeling really great the last 4 days. Maybe a little tired here and there but that was to be expected. I've been working out everyday for 30 minutes on the elliptical trainer. I try to go first thing in the morning as soon as I finish my Breakfast. Today it hit me like a ton of bricks. I feel exhausted and just generally crappy. I'm going to take a rest from the gym tomorrow.

My question is: If I'm only eating 800 calories and then burning 500 calories at the gym, should I eat another extra 500 calories to make up for the work out? I've tried to call my nutritionist but she had left for the day and it's friday.

Any help would be appreciated?