I monitor all items on my insurance policies and recheck after any changes are made.  I’ve got good insurance but mistakes can happen or a correction doesn’t go through correctly.  It is rare for me to find a mistake but it happens.  
When I crashed in 2011 the 3 days in ICU, 5 days upstairs in a regular section, along with lab work led to the initial invoice (but not the last) which listed over $47,000 in charges.  That did not include the many MRI’s, CT’s and xrays that we’re done, nor did it include the doctors fees.  That was just the hospital rooms and care, which I needed greatly.
Medical expense adds up FAST.