It's certainly intriguing for a beginning. There's not enough there to properly say anything concrete about except your writing style, which is very nice, well described, not to prose heavy, and I enjoy that. :)
The concept of the story, from what I can grasp is: I'm guessing Harry went mad, flew off the handle, and has gone round the twist or something? So, now he's in St. Mungo's? Did Ginny die? That could do it if you're going for cannon. With fannon, it can be anything. I love fannon, but cannon twists are great too.
In the past, I've had plot bunnies nip at me that include psychiatric wards as well - most of them are incredibly dark and insane and I've refrained from writing them due to disturbing everyone within my vicinity. Either way, I'm interested to see where you go with this. So far, even though there's not much, it's good.
Keep going! :)