The listener who knows your history can hear a small change others would miss.

Long acquaintance turns tiny signals into information. A slight flatness in your voice means nothing to a stranger and a great deal to someone holding years of comparison, which is why old friends ask what is wrong before you have decided anything is. That takes time to build and cannot be replaced by attentiveness, and being known is partly a matter of somebody having a long enough record of you.

Keep contact with the people who hold that record, even when there is nothing to report. When one of them asks whether you are all right, take the question seriously rather than deflecting it.