When on a VLCD you can expect your energy levels to be lower than normal, even when in deep ketosis. Due to the lack of glycogen and water in the muscle, performing too much exercise will actually lower your metabolic rate without increasing fat/weight loss. You would benefit by doing 3 to 5 sessions per week of low intensity Aerobic Exercise.
When exercising it is important not to train too intensely. You are fine to train at 60 to 70% of your MHR (Maximum Heart Rate). Maximum heart rate is determined by your age.
Most gym equipment will have sensors for you to see your heart rate or alternatively you could wear a heart rate monitor.
Suitable types of aerobic exercise includes:
Cycling (up to 10mph), golf, low impact aerobics, swimming and walking (3mph).