This happens between season 2 and three. In this version Christopher and Lorelai never slept together. Rory has just left for D.C. and Lorelai is lonely. It's about midnight and the phone is ringing. Luke rolls over and answers it.
"Hello?"
"Luke it's Lorelai."
"Good bye Lorelai."
"Luke please don't hang up."
"Why?
"I'm sorry. I'm sorry.""Lorelai what do you want?"
"I want you."
"What?"
"Will you come over?"
"Why?"
"Please just come over."
"Fine Lorelai. I'll be over in a couple minutes."
"Thank you."
Luke gets there about 5 minutes later. Lorelai greets him at the door.
"Hi!"
"Lorelai what are you wearing?"
"Lingerie."
"Why?"
"I'm trying to seduce you."
"Huh?" Luke murmurs in confusion.
"You heard me."
"I didn't come over here just for you to tease me."
"I'm not teasing you. Now come in here before the neighbors see you." Lorelai says as she pulls Luke into the house and flings the door shut.
"I'm confused."
Lorelai kisses him and then asks, "Are you still confused."
Luke simply shakes his head. They end up upstairs in Lorelai's bed. Lorelai wakes up in the middle night and sees Luke next to her. She shakes her head. And mutters "What did I do?" to herself. It never occurred to Luke how drunk Lorelai was. They were both lonely and that was apparently enough for them. When Lorelai wakes up Luke is gone. Luke and Lorelai sleeping together doesn't change the fact that they're still fighting, so they don't talk to each other at all during the summer. Lorelai also fails to mention to Rory that she and Luke slept together.
After dream sequence in 3.1: instead of calling Rory Lorelai frantically searches for a calender. She finds it, looks at it and then panics. She drops the calender and runs down the stairs, grabs her keys and gets into her car. She drives 30 minutes to Hartford. Then she drives around Hartford for another ½ an hour looking for a 24 hour drug store. She finally finds one and goes in. As she is looking at the shelves of pregnancy tests she realizes she's still in her pajamas. She just shakes her head and grabs the next pregnancy test she sees. She reads the back and then grabs another one. 10 minutes later she goes to the counter with 5 pregnancy tests.
"Will that be all?" The pale teenaged girl with a nose ring and purple hair asks.
"Are you serious? Of course that will be all."
"Ok lady you're total is. $67.83." Lorelai pays and then goes home. As soon as she gets home she runs to the bathroom and pees on every test. She sits down with her head against the bathtub while she waits for the results. She ends up falling asleep. When she wakes up the sun is in her eyes and she only has 15 minutes before she has to be at work. She runs up the stairs and gets dressed, she has 5 minutes left to spare so she makes a pot of coffee. She goes in the bathroom while she is drinking her coffee to read the tests. She looks at them carefully. She goes to the first one and it's positive. She slides down the counter to the second one and it's positive. She quickly glances at the other three and they're all positive. She then looks at her watch and she's late.