black in

Probably derived from (and as an antonym to) black out.

black in

1. (intransitive, uncommon) To regain or return to consciousness or attentiveness after having blacked out.
   • 2016 February 9, Andrew Pyper, The Damned, Simon and Schuster, →ISBN, page 77:

     Willa and Eddie barely left my side as I blacked in and blacked out over the—what? Days? Weeks? Time is unreadably stretched out on the serious postsurgical wards. It's hard to say what's a day or what's a night […]

   • 2020 March 17, Isla Stone, The Art of Determination, Balboa Press, →ISBN:

     I blacked in and out – I can't remember why he showed me the rooms. I didn't know where Antonio or the rest of his friends were, but I was too spaced out to care. Finally, I blacked out completely. When I became conscious again, […]

   • 2022 June 14, Lisa Taddeo, Ghost Lover: Stories, Simon and Schuster, →ISBN, page 129:

     She blacked out maybe, and when she blacked back in, she looked again at her screen. The eyes of the love of her life were startling, truly. His eyes did not betray him. But Grace knew now, where the good people were.

   • 2022 July 27, Safiya Nygaard, “I Made Custom Hard Candy From Scratch”, in YouTube‎^[1]:

     I just blacked back in, why is there an anvil in front of me?