I left college in the last semester (did not finish), but the college "transferred military experience to credits" and gave me a diploma. Normal? When I was in community college (2016), I wasn't on good terms with the school. I was harassed occasionally and complained about it very forcefully to representatives of the administration. I passed my classes, but didn't do homework and had an average GPA. In my last semester, I decided to stop going due to continuing issues with the faculty.

After a few months, I got a diploma in the mail. I called them and asked about it and they said it was all on the up and up, and that the VA representative had taken it upon himself to transfer some of my military experience into credits (my remaining requirements were very basic, like P.E.), which is what pushed me over the edge. 

I still have a hard time believing that I could graduate without knowing it. The VA rep was new and had recently replaced the old one, and I'm stoked he took it upon himself to transfer those credits over, but I am curious if this is a normal thing? Has this ever happened to anyone else? Am I worrying too much? I don't want to look a gift horse in the mouth, but I also am afraid there could have been some mistake.

The reason I'm worried about it now is that I want to go back to school for a CS degree in the near future now that I've matured a little and have a better idea of what I enjoy learning. If there's any chance I need to be worried about my previous degree I want to know about it.
I still have a hard time believing that I could graduate without knowing it. 


Me too. I would request a transcript and perhaps investigate to see whether "transferring military experience to credits" is something that routinely happens. It would be nice to document your concerns and get a written response from the college saying that everything is on the up-and-up. When documenting everything, I suggest not going into detail about your issues with the teachers; that is a separate issue.


  I am curious if this is a normal thing? Am I worrying too much? 


I can say that it is entirely abnormal for well-ranked, 4-year colleges in the US. However, community colleges are a different beast. While I can't say anything for sure, I can speculate:


They may have wanted to boost their graduation rates, and looked for "almost-done" students that they could convert to "done"
Perhaps your VA rep is just an awesome guy who helped you out. 
Maybe there were legal issues with the harassment case. 
Or, it's possible that something improper was done, and it will eventually cause problems for you. 


Short answer: I suspect all is OK, but I would still try to document what happened and get the college to state in writing that your degree was not awarded in error.

Edit: I do agree with the other answers that you should proceed with your application to 4-year schools; don't let this slow you down. I just think it's worth protecting yourself...for example, the diploma-generation system could be different than the degree-verification system, and they might disagree about whether you finished...best to have the whole thing documented in case something comes up.