Is taking 2 excedrin PM's nightly dangerous for my health?

Taking any medication on a regular basis is not to be recommended unless under a doctors orders so you can be tested for side effects etc. As I am not familiar with this drug I am afraid that is the only advice I can give. If it is a sleeping tablet then it is possibly ok for a short time but I would not recommend it for long term use. Talk to your local chemist / pharmacist for some more advice