If fatal familial insomnia is running in my family, would I have known for it by now?

Your family does not have this, otherwise, you would have known about it. This is extremely rare and only a tiny number of people have this. Two nights of insomnia means just that - there are factors going on in your life which are stressing you - fatigue, too much caffeine, irregular sleep patterns, too much light in the bedroom, etc. Taking some benadryl 1 hour before bedtime will give you restful sleep and will help you get back into a more normal sleep cycles. And, consider doing some exercise such as walking briskly during the day or very early evening which gives you more quality sleep at night.