"I was pregnant the whole time, so on set, I would worry," Pressly, 31, tells PEOPLE. "I remember thinking, 'Oh god – I'm Joy during the day more than I'm Jaime! He's gonna think his mother is crazy! A crazy, redneck, trailer park woman!"
Now 22 months old, Dezi James thinks nothing of his mom's daily transformation into character.
"He'll come to the set and my hair will be all crazy and he doesn't even flinch," Pressly says, "like, 'Oh. That's mom. That's fine.'"
The Emmy winner dedicated her new book, It's Not Necessarily Not the Truth, about her journey from a small town in North Carolina to Hollywood, to her son, whom she calls "the love of my life."
An Always-Excited Look"I always knew he was a boy," she says. "It's a different kind of love. When your son looks at you, he looks at you like there's no person in the world more beautiful or perfect, nobody else who can make him feel better when he's upset or sad or sick. He's always excited to see you when you come home, and always misses you when you're gone."
Like his dad, Pressly's former fiancé, deejay Eric Cubiche, 34, Dezi has always had an ear for music – even in utero.
"Babies are nocturnal when they're inside you, so right when you lay down, they wake up and it's like Dance Party USA," she says. "So I made a playlist for Dezi on iTunes, put it on my iPod, and every night would put earphones on my stomach to fall asleep."
For more on Jaime and Dezi James, pick up this week's PEOPLE, on newsstands now