Going down hill

I'm 15 and recently life has just been an uphill battle. My grades have been slipping a little and I've really disappointed my parents. I used to be an A students and 'gifted kid /perfect child'. The worst part is I really tried my hard but my best just wasn't good enough for them. Now I feel like a failure and have almost no motivation to do anything because everything is so overwhelming and anxious but I feel guilty for not doing anything. My parents think I'm lazy because somedays I don't do anything and just lay in bed. But I'm just really tired and brunt out from everything. I want to be happy like I used to be but I don't know how...