After washing Negel Vaser you may drink. There is no need to say Birchas Hashachar beforehand if you will be going back to sleep. See also here: https://asktherav.com/4239-if-one-is-awake-in-middle-of-the-night-after-sleeping-earlier-and-is-going-back-to-sleep-but-is-still-up-at-the-time-of-alos-hashachar-can-one-drink-or-eat-then-0r-do-they-need-to-say-brachos-fir/ …
