Yes! You are definitely not alone!
My son (age 25) is also 5mo. down the track with PCS (injured at work, symptoms began to appear 70hrs later). He kept working for a couple of weeks, not realising what had happened.
He feels that he was gradually improving but that his symptoms have become worse -- including headaches, severe lightheadedness, gasto-intestinal issues, neck-shoulder-back-abdominal pain, blood pressure abnormalities, variable heart rate, fatigue, noise & light sensitivity, vision problems (convergence).
What we have learned is that mTBI can result in what they call 'the primary insult', which is the actual damage to the brain, as well as the 'secondary insult', which is the brain's reaction to this -- which can produce a 'metabolic cascade' of various responses. Variable heart rate is among these.
I'd say a crucial thing is to get the best medical investigations you can see if there are any problems that can be identified. Then you will know what a recovery plan might look like.
Good luck, & best wishes from a fellow Midwesterner, now in Australia.