It does take some time to adapt to low carb but if you weren’t already exercising before you don’t really have anything to compare your energy level to, so you couldn’t necessarily say it’s reduced because of adapting.
However, you will benefit from supplementing sodium prior to working out.
Hopefully your doctor is aware of the increased need for sodium on keto and has you supplementing already.
https://m.youtube.com/watch?v=WNV0GJcrqp4

You will probably have to slow down for now... and it will likely take 8-10 weeks before you are fully "fat adapted."

Generally, a low carb, low calorie, and low fat diet (PSMF type diet) is either for those who need to to lose a whole lot of weight or for body builders, models, etc. trying to lose the last few lbs. of fat very quickly for a photo shoot or contest. In either case, it isn't a long-term approach and it is an advanced dieting practice... so I'm glad to see you are consulting with a physician who specializes in fat loss.

"Bonking" or "hitting the wall" is a reaction that athletes experience when they run out of glucose. It's mostly mental because your brain / central nervous system is only capable of either using glucose or ketones. Endurance athletes who eat carbs regularly will sometimes bonk after going through blood glucose and glycogen during a long event.

Like I said, this will take weeks to adapt for cardiovascular activity:
The first thing that will happen is you will use glycogen to supply glucose to your brain and muscles.

Next, you will start making ketones, which can be used by muscles and your brain. They will fight over these ketones for energy to supplement the small amount of glucose available. You will probably notice this when exercising during the 3-5 week time window. There is no shame in slowing down... you will need to slow down, in fact, to avoid bonking.

Finally, your muscles will start to directly oxidize fat for energy at higher and higher intensity levels. Though fat is used to make ketones (our liver does this for us), free fatty acids and ketones are not the same thing. When we get to the point where our skeletal muscles oxidize free fatty acids, ketones are freed up for our brain. Our brain and muscles are no longer fighting over ketones.

*A bonus to becoming fat adapted is lean tissue (including muscle) preservation. The traditional belief from most bodybuilders is that insulin is the only thing required for protein synthesis, and they think eating carbs to cause insulin release is essential. In fact, insulin and leucine are both part of the process and counter-balance each other. In fact, leucine is primary and insulin is just a 'helper' in protein synthesis. More leucine and less insulin works better than more insulin and less leucine. When fat adapted, our muscles 'eat' less leucine for energy since ketones are available and have a similar carbon structure. This is why fat adapted athletes have more leucine available and why eating a low carb diet causes more weight loss to come from body fat and less from lean tissue when compared to the same calories on a higher carb diet.

That’s really low-calorie. Have you talked with your doctor about what kind of workouts you have planned? I’ve found (7 weeks into keto) that I’m working at a lower intensity than I did before—I could walk all day if I wanted, but box burpees are out of the question for the time being. It sounds like your diet is a lot more restrictive than it needs to be just for low-carb and/or weight loss, which makes me concerned there might be other factors your doctor knows about that would be relevant to how (and if) you should manage workouts.

@janette130, somewhat like @TheMerryMermaid I lost 35 lbs doing low carb and low fat (definitely adequate protein, though) with no workouts - just brisk walking, snowshoeing, x-country skiing for enjoyment but not to any sweat stage, winter 2013/14. Cals were between 750-900/day.
It took me 12 weeks to do that. I did not lose hair or develop heart palpitations. I was very conscientious about my vitamins including potassium (in my case). To be included every day was 4 c. of LC vegetables. When I finished losing my weight to goal I upped the fat and slowly upped carbs to find my maintenance level. While losing it was suggested to me that if I chose to exercise more, I needed to add a bit more food (protein and a few more healthy carbs; you will be getting extra fat from body reserves, remember). Add a bit more if you need the energy. If everything is still working well, no problems as long as you realize that you will need to move into a maintenance phase slowly, once you have reached goal, and up your intake to balance your energy output without losing or gaining weight.
It can be done in a healthy successful way but of course n=1 so be very aware of what your body is telling you.

800 calories total for the day? when working out? no this is awful advice, I don't care if a "doctor" told you to do it, its unhealthy and a recipe for disaster. not only will you "hit the wall" you will be damaging your body if you plan to do this for any extended period of time.

I'd spend some time searching around the group here reading threads from people who've had success.