Waking up in his underwear among strangers was the least of Dave Sanderson’s problems.

As Sanderson came to his senses on the shore of the Hudson River in Hoboken, N.J., his lack of appropriate clothing paled in significance beside the circumstances that had landed him in that situation.

Sanderson, who spoke Friday during a program at Lake Prince Woods, was the last passenger off US Airways Flight 1549 after it ditched into the Hudson River on Jan. 15, 2009.

Sanderson should have been on another flight home from LaGuardia Airport to his wife, Terri, and their four kids in Charlotte, N.C., but he seized a chance for a quicker return from a business trip and wound up on Flight 1549.

“I truly believe I was meant to be on that flight for a reason,” Sanderson said.

That afternoon, he took his seat four rows behind the left wing, slid his briefcase under the seat in front and flipped open a magazine.

He wasn’t listening when crewmembers ran through the safety procedures. “I guarantee every time I get on a plane now, I do,” he said.

About three minutes into the flight, Sanderson saw flames leaping out from under the left wing. The Airbus A320 had struck a flock of Canada geese.

“To this day — five years later — the one thing that stays with me: It was so quiet. You could hear a pin drop,” he said.

In fact, besides Capt. Chesley B. “Sully” Sullenberger announcing, “This is your captain; brace for impact,” 90 seconds before expertly gliding the plane onto the Hudson just off Midtown Manhattan, one woman’s quiet prayers were the only sound from anyone, Sanderson said.

“I had my head down, and the entire movie of my life started going through my head,” he said. “I saw everything, from Little League baseball to my first girlfriend. I saw absolutely everything. I had total clarity.”

The plane glided over the George Washington Bridge and — for passengers — descended into the unknown.

Sanderson asked God to forgive him his sins. He retrieved his wallet from his briefcase and shoved it into his pants. “I wanted my kids to know who I was,” he said.

“Then I put my head down.”

The impact was hard. Sanderson saw light coming out the window. “I knew I had a shot,” he said.

Water immediately began entering through the floor and from the back, reaching from the ankles to the knees, depending on one’s position in the cabin.

The tops of backrests had snapped off as the 150 passengers were thrown forward then ripped back, and people jumped onto seats, ran along rows and climbed onto the wings.

“My thought was get to the aisle, get up and get out,” Sanderson said. But the voice of his mother told him what she had told him often before she died.

“If you do the right thing, God will take care of you.”

“The right thing was to take care of other people first,” Sanderson said.

He was the last passenger off the plane, because he helped others first. But the real heroes of the day were the first responders, he said, including the ferry crews that mobilized immediately. He also hailed the American Red Cross for the assistance they provided passengers.

Sanderson jumped into the icy Hudson after a tugboat accidentally hit the plane and water sloshed up his back. He swam to the closest boat and climbed the ladder over the side, strong arms grabbing him from above.

“This is the moment when all the adrenaline goes out of your body, and I was so cold,” Sanderson said. “I couldn’t breathe; I couldn’t move.”

On dry land in Hoboken, N.J., Sanderson realized he was dressed in only his underwear. A girl next to him was completely naked. “Everybody’s next to each other on the floor naked, and no one’s talking,” he said.

Because he was suffering from hypothermia, his temperature and blood pressure were so low an imminent heart attack or stroke was feared. With frozen kidneys and stomach, he couldn’t even relieve himself.

Sanderson said he still has bruises on his legs that were frozen there, and scars where his underwear was ripped off. He wears glasses now after getting jet fuel in his left eye.

The first audience he spoke to about his experience was a men’s group at his Methodist church. Several other church engagement events eased him into his current vocation.

Soon to be the sole author of a second book after co-authoring the first one with other Flight 1549 passengers, Sanderson said he stopped counting at 525 speaking engagements.