WhenJohnny Galeckiagreed to guest-star on the reboot ofRoseanneand reprise his role of David Healy, the actor didn’t know what to expect.

Walking onto the set “was most surreal experience I’ve ever had,” theBig Bang Theorystar tells PEOPLE. “I was excited to see everyone in the same room again but what I wasn’t expecting was walking ontothatset again, which the designers recreated to a T.”

The actor, 43, wasn’t surprised to see familiar items like the Conner family couch, “but the little things like the knobs on the stove, it’s just weird how it opened up your brain to memories you didn’t even realize existed in your psyche,” says Galecki, who starred on the show from 1992 to 1997. “It was very, very surreal and emotional and celebratory. It was like going to your 20th high school reunion except all the people are your heroes, not the bullies.”

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Galecki, who was 16 years old when he started working on the series, insisted he felt “great relief in the fact that this character, 21 years later, was still dormant and resurfaced almost immediately,” he says. “It’s kind of creepy, those characters they reside in you for a long, long time.”

And while he typically doesn’t watch himself in anything, Galecki did ask his siblings and mom to watch his episode “because we were such big fans of that show before I had anything to do with it,” he adds. “And I knew I was going to be proud of it.”

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As for David possibly appearing in future episodes, Galecki is leaving the door open. “I hope so,” he says. “It’s a lot of scheduling and a little bit of politics because it’s two networks but everyone has been supportive. I most probably would not be onBig Bangif it wasn’t forRoseanne. And they understand the emotional attachment and this high school crush that I still have on this character.”

With both shows now on hiatus, Galecki is spending the summer performing in a duet band in smaller venues around the country. “I’m working with these wonderful musicians,” he says. “We’re secretly peppering our way across the country and opening for some great artists under pseudonyms. We decide who we are going to be 10 minutes before the show every night.”

The scientists featured in the series “truly are the people molding our culture and shaping our future,” Galecki adds. “This show was a very, very fun-loving way to try to encourage even more kids to do so.”

source: people.com