The Pennsylvania legislator -- who was just elected to the U.S. Senate this past November in a tight race against Dr. Oz -- talked to CBS on camera a couple days before he was discharged from Walter Reed in D.C. ... where he's been receiving treatment since February.

Fetterman was released from inpatient care on Friday, and now says he's in remission for his depression. Here in this interview, he goes on to explain that he's looking forward to making up for lost time ... especially with his family.

As it turns out, JF actually went into the hospital on his son's 14th birthday -- a memory that brought him to tears ... as he didn't want his kid to remember that moment with this.

Unclear what sparked Fetterman's depression, but it sounds like he'd battled it for years ... even before he ran for the open PA Senate seat. The news report also suggests his stroke from last year -- which has affected his ability to communicate -- might've played a part.

One big revelation ... Fetterman says, at one point, he was indifferent about living or dying.

Another interesting nugget from this sit-down ... the Walter Reed docs have found a serious new hearing deficit in him, although it's not said explicitly if it's permanent or not. In any case, it sounds like Sen. Fetterman will continue using closed captioning devices for the time being -- which he'd already been doing since coming back from his stroke recovery.