Should I use a fixed navigation in a one-page site to improve usability?

Client wants a single page website with a lot of stuff to show. I have no images to show, only text and maybe a couple videos.

This is a first version I've been working on:

Ok, so my question is: Should I use a fixed navigation in a one-page site to improve usability?

The page is too long and I'm afraid users might feel lost if they decide to scroll down. Is a fixed menu a good way to approach this problem?