Serge asked
What are side effects of this drug?

You could check
http://high-altitude-medicine.com
which has info about Acute Mountain Sickness and acetazolamide -- and lots
of other stuff about altitude acclimatization and illnesses.

Can I increase blood acidity drinking lemon juice . . .

I never heard of anything like that helping with altitude acclimatization
(though I have heard that drinking more plain water is a good idea). And
maybe it's not just addressing blood alkalinity that's the point -- it could
be that the specific _way_ that acetazolamide does it is important --
dealing with the CO2 issue.

Ken