I understand you very well because in Spain, most people value a lot the stability of a permanent position. And permanent roles are quite rare these days in Spain.
Whenever I face these kind of decisions, I found that fear to the unknown is what hurts me the most. Therefore I try to make a risk assessment, that usually clears my mind.
Firstly, I think that if your side project is already making some money, it is likely that if you put the hours, it will work out and make more money, probably enough for you to live out of it with your current condition.
Regardless, you have savings and there are lots of opportunities if you want to come back to the standard job market, specially for an experienced leader with a competent level of English. So the risk of failing to come back is quite small.
Now, about your discipline and motivation, those are very tricky and I think they are my greatest fears, but anyhow it'd probably be a good opportunity to learn and master those skills.
By the way, I decided that from August, I'll work full time on my project for a few months and see how that goes. Feel free to contact me www.carlosbaraza.com!