Well, to be honest, as a small business owner I have to admit that nothing keeps me up at night, I have learned that worrying accomplishes nothing, and I do my problem solving and strategic thinking during the day then let it go at night.
There will always be difficult situations or problems that arise that cause distress and need to be dealt with, issues with clients or customers that are way beyond the norm, like if you are being sued or you are suing someone.
Anything to do with money, revenues, taxes, payroll, cash flow and the like if there are problems in that area and that tends to be dependent on existing and new business. For without customers you have no revenue.
The other thing is your employee satisfaction, productivity, loyalty and camaraderie. If there is dissent or friction in the office, if employees are sabotaging another, it can be hell on earth. When employee issues arise, they can cause big headaches.
So these are the areas that would be the cause for consideration if they are not going well.