At my last job, a lot of people in the office would go for a 30 minute walk at lunch time. It was very common.
For me, I don't think it's the "fresh air" that helps me, but just the muscle exercise.
This. Your blood is 95-99% saturated at all times, unless you have a severe, life-threatening illness. How you breathe or whether you go out has little or no effect. The muscle exercise, on the other hand, has several positive effects.
As for sugar, that's pretty normal since the non-child brain which is not "trained" (this takes several weeks) to live on keto-bodies has no other energy source but glucose. Though of course eating what you call "chocolate" (chocolate normally does not contain large amounts of sugar) is the exact wrong thing. Rather than give your body sugar boosts followed by "hunger", you should have meals which provide a constant supply of energy thoughout the day.
As to me incidentally I have some illnes related to my breathing
system, i do not know what it is it seem to me like something like
candida infection in lungs and throat or somethink, but the
medicine people say that they see nothing - got tomography and it shows also nothing special (its a long story I feel it more than 10 years now - not suitable to go into detail here I think)
I say incidentally because my oxygene demand seem to be not quite related to that I just feel I need brath good quality air to think better, my head need such breathing for rest - and a walk
for oxygene is a must for me specially when coding ) feel much better there and can back to work (without that It goes much worse)