POTUS sat down for an interview with Howard Stern on his SiriusXM show Friday, and spoke about his first wife Neilia and their infant daughter dying in a 1972 car crash ... admitting he briefly thought about suicide.

Biden says a person doesn't have to be crazy to consider this ... adding he even thought about jumping off the Delaware Memorial Bridge ... but ultimately decided against it because he had two other children, Beau and Hunter, to think about.

The Prez clarifies he didn't contemplate suicide because he wanted to die ... but, instead, because life had knocked him down, and it didn't feel like he'd ever truly be able to climb back to those same heights.

JB also says he almost drowned in his sorrow after Neilia's death ... regularly pulling out a bottle of scotch, but never taking a pull. Biden often talks about abstaining from alcohol because of rampant alcoholism in his family.

46 says he never thought he could find happiness again -- but that all changed when he started dating Jill Biden ... something he says his sons were intricately involved in at the time.

There's more ... Joe also lifted the lid on his younger years during the interview ... admitting he once got smacked by a bully in the neighborhood -- and his mom told him to hit back, which he did. Biden says he ended up bloodying the kid, and his mom gave him a quarter.

Biden's interview came a day after the New York Times made a statement blasting him for avoiding media interviews. So ... maybe a bit of damage control here.

Either way, Biden's letting voters see a whole new side of him as the election approaches. We'll have to wait and see if this new honesty pays off.