[grandalf]

If it was an error you expected, then you should handle it using application logic. If you use a programming language with exceptions and one gets thrown and you use it for flow control, that doesn't mean the sever is broken.

The API consumer doesn't need to think there is a problem, since you might have ways of handling it in a more subtle way. Maybe when your DB connection times out you send an application specific message that includes the number of milliseconds to wait for a retry. You don't have to let the shit hit the fan and return a 5xx any time something slightly exceptional occurs, 5xx is for things that are truly exceptional and for which you have no helpful information for the consumer about what to do.