Is it bad to take asthma medicine if you're not diagnosed with asthma?

When I was younger, a few times I was so congested I could barely breathe, so my parents had me use my siblings' asthma nebulizer (they both had pretty severe asthma). Anyways, I'm older now, if I get so sick again that I have difficulty breathing is it okay to take OTC asthma medicine (primatene tablets?) I don't have asthma, but I remember the asthma meds working wonders when I could barely breathe.