I [20M] have been working at my new job for about a month and a half now, and I'm really enjoying it so far. After job hunting for months, I was overjoyed when offered the position, especially since a majority of it involves being given a daily routine to work through entirely on my own, meaning I rarely have to interact with others and am in total control of my given tasks/the pace at which they are completed. Occasionally I am assigned extra work throughout the day via pager, but for the most part I am the boss of my own schedule. 

However, now that I've had enough time to familiarize myself with the work, lately I've been completing my ENTIRE daily routine within the first 3 or 4 hours of my 8-hour shift, and am left with several hours of free time if I end up with little to no extra assignments, which is often. I'm not rushing through it on purpose, and I'm not doing it sloppily. The needed skillset for the job is just something I have personal experience with, so I can get through it quickly. So far I've filled this extra time wandering between storage closets or empty conference rooms to just sit and wait for time to pass. I'm constantly on edge throughout, anxiously checking my pager every couple minutes for any messages from a supervisor, worrying that I might miss something, even though it plays a notification sound when I do actually receive something that needs my attention. Worse is when my steadily increasing paranoia insists that somehow they'll know I'm sitting around and decide to end my employment then and there out. 

I usually end up on my phone, reading or listening to music, but I'm unable to relax in the slightest when I'm not doing anything that might be considered productive. By the end of the day, I end up feeling horribly guilty when I drop off my keys and pager. I feel like I've been doing something wrong and everyone knows it, even though all my supervisors usually have to say at the end of my shift is "thanks *insert name here*, see you tomorrow" and little else. I'm exhausted, not only because my job is physically taxing, but because of how drained my anxiety makes me. Again, I love my job, but I no longer have the mental energy for anything outside of it. 

I don't want MORE work to do during this free time, so the last thing I want to do is call a supervisor and beg for more to do. The job itself is very physically taxing, so I'm grateful for any and all downtime, especially since I have joint problems that often flare up on busier days. If anyone has any advice for how to deal with my anxiety, or even just how to increase my confidence in a workplace (this is the first job I've had in such a professional environment, and struggle to feel like I deserve to be there in the first place), I'd be extremely grateful to hear any helpful suggestions/advice. Thanks in advance. 

TLDR; I finish my daily tasks at work halfway through a shift, and feel so horribly anxious taking this ndjfk that I end up twice as exhausted by the end of my shift. Any advice would be greatly appreciated.