The actor's spouse revealed the reason behind their family's travel to Vermont, saying they needed to get away from all the madness following the fatal accident ... this according to the NYPost, who snagged a one-on-one interview on Saturday, separate from their pap encounter.

It also sounds like she was tasked with finding a solitary place for them all, telling the outlet she drove around "an entire day" before settling on Manchester, VT ... and before Alec and co. eventually joined her. She says they needed to get away to "mourn Halyna's death."

She added, "Alec had a really traumatic thing happen, and I am trying to limit the PTSD."

HB went on to compare Alec's situation to that of a war vet or cop ... who might normally develop the affliction -- saying, "You look at what happens to soldiers and police officers when something like this happens, it's traumatic. We just came up here for quiet."

She also spoke on whether her hubby would ever act again, and the Post says she replied she was "hopeful but not certain." Hilaria also said, "He needs space for me to take care of him and his mental health. It's an awful thing that happened. Alec feels awful."

Hilaria also echoed something Alec himself said on camera -- that this sort of thing shouldn't have happened, and tighter regulations need to be in place. She's clearly standing by her man, taking to IG after their eventful weekend to post a photo of their hands intertwined.