You are unlikely to be banned from the US for a short overstay where you did not breach other terms of your entry (ie you did not work or commit any criminal act). It is possible to receive an emergency extension to even VWP admission period if you have a good reason and contact the CBP. I am not sure if it possible to do this retrospectivly however.
Until (and if) you get a special dispensation for your health issues, you are however no longer eligible for use of the Visa Waiver Program (the scheme that you used to enter the US, which is not the ESTA - ESTA is permission to travel to the US, not enter in to it). The US CBP page on the Visa Waiver Program says under its requirements section:
Previous Compliance and No Prior Visa Ineligibilities
If you have had a U.S. visa before or previously traveled to the United States under the VWP or another status, you must have complied with the conditions of previous admissions to the United States, and you must not have previously been found ineligible for a U.S. visa.
So unless you were given dispensation to stay, you have not previously complied with your visa waiver and will need to apply for a visa for future vists to the US. If you do this, you would be advised to explain and provide documentation for why you previously overstayed. You will certanly find out at this point if you have been banned.
Nobody would have mentioned any of this on your departure from the US as the US does not have any exit immigration controls. You can however check your records for entries and exits under the VWP on the electronic I94 site.
You could also try to contact the CBP directly to inquire if you are banned, I am not aware of any automated way to inquire (and can find no obvious reference to visa/travel bans on their website).