This is a difficult post to respond to Firstly, your issue doesn't seem to be anything other than social anxiety If you have to 'lose sleep' after contacting someone on LinkedIn about your product, then you are just not suited to doing a startup Secondly, there is nothing to feel bad about Vast majority of people are not suited to starting a company or working in a small startup Lots of good jobs in middle and large…
On a related note, social anxiety can be awefully crippling, I personally struggled with it for decades. The main tool that helped me overcome it was the book The Charisma Myth. Can't recommend it enough, it literally changed my life. It does take some work and dedication though.
I remember first day of speech in college when it was my turn to speak. I got up, walked out the door, and dropped the class.
It was hard to even work up the courage to post this comment. But i did. Baby steps.