You can get a finger-tip blood oxygen and heart rate indicator for about a sawbuck online, and I would recommend that you do so:

It is a mystery that has left doctors questioning the basic tenets of biology: Covid-19 patients who are talking and apparently not in distress, but who have oxygen levels low enough to typically cause unconsciousness or even death.

The phenomenon, known by some as “happy hypoxia” (some prefer the term “silent”) is raising questions about exactly how the virus attacks the lungs and whether there could be more effective ways of treating such patients.

A healthy person would be expected to have an oxygen saturation of at least 95%. But doctors are reporting patients attending A&E with oxygen percentage levels in the 80s or 70s, with some drastic cases below 50%.

Using the fingertip sensor takes less than a minute, and it is non-invasive and not painful, so checking yourself occasionally is a good thing.