Thank you for asking your query.
From your description of the problem you had a blackout and convulsion once, then one more episode of convulsion. By convulsion I assume that you had a seizure like activity. All this followed an asthma/anxiety attack.
It's very difficult to pin point to a single cause without physical examination and some tests. Anyhow there are two major possibilities A metabolic problem or a neurological problem.
Metabolic problems has to do with all the electrolytes like sodium, potassium; gas concentrations like oxygen, carbon dioxide, , sugar levels etc in the body. Exertion, asthma medication can cause derangement in these levels and body can react by convulsing or blackout. I think in your case it has to be evaluated whether any metabolic problems is causing the issues. For this some blood tests are needed. A neurological problem has to be considered if the above tests are inconclusive. You may need a CT/MRI of the brain.
So I would recommend you to stay hydrated, and eat normally at regular intervals. Avoid severe exertion for a couple of weeks. Do not take any supplements or energy/electrolyte drinks during this time period. I recommend you to visit a Physician who can evaluate your condition and do the necessary blood investigations.
Hope this helps
Please feel free to ask follow-up questions if any.