Do not ignore symptoms that may be due to low or high blood glucose. If you have symptoms that do not match the Sensor glucose reading or suspect that your reading may be inaccurate, check the reading by conducting a finger stick test using a blood glucose meter. If you are experiencing symptoms that are not consistent with your glucose readings, consult your health care professional.

During what situations/scenarios would one get "Check Sensor" messages?

The Check Sensor message occurs when the user tries to check glucose and the Sensor does not seem to be “active”. This usually means that the Sensor has come loose or has not been applied properly. If it appears to be applied properly, the user should try starting it again. This message will not appear once a glucose result appears.1

Reference

1. FreeStyle Libre flash glucose monitoring system User's Manual.