If you need an ambulance, call from a landline if at all possible. That way the EMTs or Paramedics will automatically know the address, even if you get cut off. Other countries have their own emergency numbers; “911” is for the U.S.
Open your door and keep it ajar, certainly if you’re alone, but also if you’re busy attending to the sick patient. If you pass out, EMTs arrive, and the door is locked, they have to call the police to get in. Police won’t break in until they have enough back-up to secure the site. Takes time, may be too late.
If you’re so sick you can’t talk, tap slowly & repeatedly on the phone. Listen to see if the operator says something like, “tap twice if you’re sick.” You could try 3 rapid taps, 3 slow ones, 3 rapid ones — that’s “SOS” in Morse code, though probably nobody knows it any more.
If you’re not that sick, how do you know if you need to call an ambulance? Basically, if you think a person might possibly have a disease that could kill or permanently damage them sooner than they could get to an emergency room on their own. Some examples are heart attacks, severe trouble breathing, meningitis, stroke, broken neck, new major confusion, poked a knife in eye… (you get the idea).
Other conditions might clearly benefit from same-day diagnosis & treatment, in an urgent-care setting or emergency room, but don’t really require 911. PLEASE, don’t call. When ambulances are overwhelmed with non-urgent calls, they can’t get to the really life-threatening cases in time.