I'm sorry your grandfather died BCBoy, but there's no reason for things to go downhill, unless you let them.
It's ok to feel sad and to grieve...it's natural to do that. Healthy even - it's tough and it's sad to say goodbye to those we love, but it's part of life.
Don't be tempted to avoid grief by doing whatever your drug of choice is - I'm guessing your family needs you right now.
best wishes
D