(CNN) -- The decision to take to the Senate floor with questions on drones was a last minute one, Sen. Rand Paul explained in an exclusive interview with CNN Thursday, detailing how he wasn't totally prepared to remain standing for thirteen hours straight.
"We had no plan and I had the wrong shoes on, my feet were hurting the whole day," Paul told CNN Chief Congressional Correspondent Dana Bash, adding that since the Senate leadership typically decides who speaks on the Senate floor, it's often difficult to begin a traditional filibuster.
"One of the reasons filibusters don't occur is because they carefully guard the floor from letting it happen. And it was left unguarded," he said.
His voice was still recovering from his epic floor remarks, Paul said, though he got a break from a bevy of Republican senators (and one Democrat) who joined in during the day. And he speculated he may have "lost a few pounds" by only eating an occasional candy bar - which cameras caught him noshing on throughout the day.
"There's a candy drawer, and if you go to the candy drawer, you can sneak around and get a candy bar," he said. "But I see you caught me with half the candy bar in and half out of my mouth. My wife said can't you chew with your mouth closed on the floor?"
The grueling conditions are all part of the rules of a traditional filibuster, which Paul admitted were demanding.
"It's not easy. My feet were hurting by the end of the day. You can't leave the floor and you can't sit down. So you can't use the restroom or do anything like that," he said, admitting the staff in the chamber are often more knowledgeable about restrictions than lawmakers themselves.
One of his tips? "I decided to drink very little water and have no caffeine."
Paul hasn't been without his Republican critics, including the conservative editorial page of the Wall Street Journal, which Thursday urged him to "calm down."
"The U.S. government cannot randomly target American citizens on U.S. soil or anywhere else," the paper's editorial read.
"The Wall Street Journal is right on a lot of issues and they're wrong on this issue," Paul responded in his CNN interview. "The problem is if I call you an enemy combatant, how do we know if you are or aren't? That's just me calling you and accusing you of a crime."
"Should there be enough power by any politician, Republican or Democrat, to just say you're an enemy combatant and a hellfire missile drops on your house?" he asked. "That's what they're saying. With every fiber of my body, I believe that's unjust and unconstitutional."
Paul revealed the White House had reached out to his office, though the Kentucky Republican didn't offer additional details of his communication with the Obama administration.
Later Thursday, White House Press Secretary Jay Carney said U.S. Attorney General Eric Holder sent a letter responding to Paul's questions about the legality of drone strikes against United States citizens.
The letter, Carney said, addressed the question about whether the president has the authority to use a drone loaded with a weapon to kill an American not engaged in combat on U.S. soil.
Reading from the letter, Carney said "the answer is no."
At 1:15 p.m. ET, Carney said the letter was sent to Paul "within the last half hour or so."
In his CNN interview, Paul speculated that Obama and he could have more in common on the issue than it may appear.
"When Barack Obama was a senator, I think he would have been standing with me last night," Paul said. "I think he, like [Democratic Sen. Ron] Wyden, would have come to the floor and supported me yesterday. I think he's either forgotten or needs to be more explicit in what his beliefs are."