During one of my previous background investigations, the interviewer had noted on my file that I had no questionable gaps in my employment history that I needed to explain to them. At the time, I had been unemployed for near 6 months, which I would consider a lengthy gap in employment (although not quite a "gap" yet since there was no starting point on the other side yet). There was also a 1-2 month gap at my previous job where I had quit and then re-applied for a different position at the same company.
Is there any normal period of time being unemployed that will cause employers to start questioning why you were unemployed for so long? How much do gaps in your employment history affect your chances at getting a job?