For anyone that have regardless caught the virus, the critical days are day 5 to 10. It can suddenly turn to worse, even if you were mildly sick before that, or had recovered on day 5.
Reaching 14th day is what we can mark as : the worst is behind us. inshaAllah.
https://www.nytimes.com/2020/04/30/well/live/coronavirus-days-5-through-10.html