Death is the only guarantee any of us have in this life Nick! I also get bouts of insomnia when I really stressed, and I think it's the body getting geared up to run away from stressful situations to keep you safe - unfortunately the majority of my stressful situations can't be escaped like that. There's no way I could run away from my mortgage, for example, but that doesn't stop me from worrying about money.
Yeah it's strange the way our bodies react with primitive impulses to problems where they're not useful. Well, I suppose it's not strange but the reactions the body has are usually more hinderance than help. Like you say, insomnia caused by money problems only tends to make me feel more stressed, rather than helping me deal with the problem.