I love how closely they huddle, and how even in sleep, or perhaps just in mutual comfort, they still look worried and worn, holding each other against the day they'll be pulled apart. I adore that Minerva is clearly a middle-aged woman and still breathtakingly desirable. (Side-note: you draw the most beautiful hair.) Snape looks like a real person here, not a caricature, and the way his hand rests on Minerva's head expresses so much cherishing and care.
This is not only beautiful; it's incredibly moving. People glimpsed in sleep are vulnerable, and these two so rarely permit vulnerability to show that it's truly a private and precious sight. Thank you for sharing it with us.