The 33-year-old actress - who plays Penny in the CBS sitcom - admitted she "didn't sleep" after receiving her script for the season 12 finale, which will be the last-ever episode of the long-running series.
She shared a photo of the script, which had "End of series" written across the front and captioned her Instagram post: "Yea, didn't sleep."
Kaley later shared a photo of her visibly tearful as she held onto her script.
She captioned the image: "Post table read for @bigbangtheory_cbs finale episode (sic)"
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Former 'Friends' actress Courteney Cox sent her sympathy to the star.
She commented: "awww I remember that feeling...and you guys have been together even longer (sic)"
And her third post showed off the pile of tissues she'd needed to dry her eyes as she went through the script with her castmates.
Kaley warned viewers to "prepare" themselves for the finale, which had left her at a "loss for words".
She captioned the post: "Prepare yourselves ... for a finale that has truly given me a loss for words [heart emoji] Our whole universe ......"
Her co-star's also found the table read difficult.
Kunal Nayyar, who plays Rajesh, also shared the final script on Instagram, and wrote: "Just read the final episode... Gnite #tbbt.(sic)"
Johnny Galecki, who plays Leonard, commented: "Roughest page ever read. XO.(sic)"
Kaley previously admitted she was planning on taking home one of the paintings from the set, as she "won't know" what she's doing without it.
She said: "There's a piece of art in the living room set - if you're looking at the set from the audience it's to the left - it has a big doughnut and a robot ... it's been there since the pilot and I'm going to take that home. It's always in my view and I've been looking at it for so many years. I think I won't know what to do unless I'm looking at it, so it needs to be in my living room."