"I'm like living another life now," he told a court in Park City.
"My interaction with my family has been more difficult and I think.... I of course... I'm desperate to be close to my family and my girls.
"But something's wrong with my essence and what I bring to the table with them. Communication is not as smooth and it's been more difficult."
Sanderson is suing the "Shakespeare in Love" actress over the collision, which his lawyers say caused him damage to the tune of $3.3 million. He filed the suit in 2019 and the case has taken this long to reach court.
Paltrow has in turn countersued, for a symbolic $1, plus legal expenses.
The actress told the trial last week that Sanderson had ploughed into the back of her.
But on Monday, Sanderson took the stand to insist that it was he who was the victim.
"I got hit in my back so hard and it was right at my shoulder blades, a serious, serious smack. I’ve never been hit that hard, and I'm flying," he told the jury.
"Last thing I remember, everything was black."
Sanderson, who before the incident had suffered vision problems and a heart attack, said the collision knocked him out.
Asked about an email he sent to his daughters about the crash with a Hollywood celebrity with the subject line "I'm famous," Sanderson said: "My head was scrambled."
"I didn’t pick my words well. I was trying to add a little levity to a serious situation and it backfired."
He did not deny sending the email, but insisted: "It's the other personality that's inhabiting my body right now."
Stephen Owens, representing Paltrow, argued that any changes in Sanderson's personality were more to do with the natural ageing process.
Paltrow was skiing with her children and her partner, Brad Falchuk.
Last week she told the court "Mr. Sanderson categorically hit me on that ski slope, and that is the truth."
"I was skiing, and two skis came between my skis, forcing my legs apart, and then there was a body pressing against me, and there was a very strange grunting noise" she said.
In his opening statement last week, Paltrow's lawyer said Sanderson is "obsessed" with the lawsuit, and that the case was a "meritless claim of false allegation."
In addition to her Oscar-winning acting career, Paltrow has forged a second career marketing wellness products on her Goop website.