Insomnia is a pretty significant mental health concern, and one that is hard to treat. It's always been a problem for me. I cope by not going to bed when I'm not tired so that I don't lie there and get frustrated all night. Insomnia is one of the major concerns with more than half of my clients too. There is a connection between circadian rhythm and serotonin and depression, and that connection is hard to break. Interventions that have to do with sleep cycles can help with depression and bipolar disorder (light therapy and dark therapy and wake therapy). Linehan mentions persistent sleep problems in her book about DBT. Apparently it is a common problem for people with BPD. Sleep is a very serious subject.