Law enforcement tells TMZ ... someone called the cops and told a dispatcher he was worried about a friend's well-being -- but never mentioned Aniston by name.

Per the cops, the caller said his friend was "not doing well" ... and supposedly alluded to seeing him on the other side. We're told the caller then asked cops to do a welfare check, providing only the address and keeping himself anonymous.

We're told authorities stopped by the address just after midnight ... where they were met by security, who was seriously surprised by their arrival.

It was during this time that police learned they were at Aniston's home ... and cops say they spoke with the actress, who assured them everything was OK and that she had no self-harm intentions.

In an attempt to avoid another incident like this one ... police say they've since noted the location and, if called again for a welfare check, plan to speak with security first before rolling out and disturbing Aniston's beauty sleep again.

However, this isn't a closed case just yet ... as we're told police are treating the call as a swatting and are now investigating the incident further.

Aniston isn't the first celebrity to fall victim to a swatting prank. Chris Brown, Nicki Minaj, Rihanna, Justin Bieber and others have all been victims of a hoax call ... resulting in a surprise police presence at their respective homes.