PS It may also help to take what precautions you can before you self harm like keeping windows open or even the door, calling someone to be with you for when the police arrive. But do try to limit blood loss and apply your own first aid/pressure if possible, knowing you will be on your way to hospital later on. Have regular blood tests too.
Do talk to your GP as well, you need help from local NHS, services and therapy whether NHS or private, though I know that secondary care services can let many down.
I think the NHS is so cash strapped and poor in places, that we don't have the option or permission to rely on it anymore ie fast ambulance and treatment times, it is a great shame.