Right now they'll probably want to test and actively quarantine you, if you really are showing symptoms.
In a more mass-spread scenario, where they can't really handle all the cases with high attention - follow your symptoms each day closely and if you're getting noticeably worse from one day to the next after the early symptoms have appeared (after the first several days), go to the hospital and seek treatment. It doesn't appear to be much different than having the flu in this regard, it's that the mortality rate and virality appears to be far higher (and a far higher percentage of patients are requiring intensive care).
There was an excellent 'inside the hot zone' article posted here on HN a few weeks ago, that interviewed a doctor in China that had directly dealt with many early cases of Covid. His input was that the people that died turned hard south in the second week after symptoms presented, and would often die in the third week. That pattern tended to repeat for patients that died. Seeking treatment at a hospital as soon as possible if you see yourself turn for the worse in the second week, appears to be critical.
The pattern you describe should be everyone's standard practice already.
If symptoms are getting worse, particularly acutely, seek medical attention.
Importantly, if you think it might be something bad (like COVID-19 or another contagious disease) make sure to make that known to the first and primary medical contacts you make as you seek treatment.
If you're older than 50, still go but take extra precautions. And take any symptoms very seriously.