Sadly, the very nature of SEO tunnel vision makes self-diagnosis impracticable. So how do you know if you have this condition? There are several ways. First, you can look for the counseling of a trusted Internet marketing consultant. These professionals have a keen capability to spot SEO tunnel vision.
You might as well use the Platonic method, which involves asking yourself a series of questions to discover the truth that's buried inside you. For instance: Do I spend more time checking my website rankings or improving my product / service? Have I invested time and effort to get better the reader's understanding upon reaching my website, or do my efforts end with the search engines?
Possibly the best way to identify yourself is to take a healthy dose of Web Reality* (no prescription necessary). A dose of Web Reality might contain comparing the number of people who come across your website to the number of people who respond to it. Yes, the good old conversion rate. You might as well make sure your website analytics program to see what the bounce rate is for people entering your website through search engines.