Lucy describes her sleepwalking experience to Mina a couple of days after the event. Mina was reluctant to bring it up for fear of causing Lucy anxiety and anguish by bringing up the bad memory. However, Lucy wasn't disturbed by the memory at all and gave Mina a detailed description of her experience.
Her memory of the sleepwalking part where she left her bedroom in her nightgown and walked through the streets, over the bridge and up the stairs to the bench overlooking the harbor near the churchyard had a dream-like quality, although she was consciously aware of a fish jumping as she crossed the bridge and dogs barking as she climbed the stairs.
However, the part where she's on the bench with the black figure with red eyes (Dracula) seems like a description of a typical near-death experience:
"My soul seemed to go out from my body and float about the air. I seem to remember that once the West Lighthouse was right under me, and then there was a sort of agonising feeling, as if I were in an earthquake, and I came back and found you shaking my body. I saw you do it before I felt you."
It's really cool how, as the reader knows that this is when Dracula is drinking Lucy's blood, she's having this out-of-body near-death experience. When Dracula is scared away by Mina's approach and Mina resuscitates Lucy, Lucy's essence returns to her body.