You have to be strict with yourself. Sleeping like that will definitely be affecting your mental health, most people dont realise just how important it is to sleep right - especially with bipolar!

As suggested Melatonin will help you sleep at night, but you must not sleep during the day. It feels hard when you are depressed but it does pay off, sometimes it takes a few months to get into a good routine but dont give up! There are some calming herbal teas or over the counter sleep suppliments that can be helpful. Sleeping too much or not enough will cause depression, anxiety and even mania.