Getting back to reading after years away is something that takes patience with yourself, because the first book you pick up won't ever be the way you remember it from high school. The real trap is choosing something too "important" - like the classic everyone says is amazing - and then abandoning it on page 30 because you feel like you're supposed to read it instead of actually enjoying it. Better to go for stories that don't demand massive concentration but still make you lose track of time.
The thrillers other people have suggested work, but here's something I'd add: it's not just the book's length that matters, it's the number of characters and subplots. A tangled plot can exhaust your brain if you haven't read in a while. Try authors who know how to grip readers without too many details: Ken Follett maybe goes too far, but writers like Tess Gerritsen or procedurals in the style of Donna Leon keep up the pace without weighing you down. Start with one of those books you finish in three or four intense days rather than one that drags on for weeks.
The audiobook someone mentioned is clever, but fair warning: listening isn't the same as reading. With audiobooks it's easy to pretend you're following along while your mind goes somewhere else. If your goal is to get back to the pleasure of actual reading, a physical book or e-reader is better for now. Once you find your rhythm again, audiobooks become a bonus, not the main solution.