I know how you feel my friend... Had a concussion more than a decade ago were a car ran me on my bike. Passed blood tests and even a few scans (CT-Scan, MRI,etc...) in the last year and every test are looking normal!

And, well. 4 year's ago I started to feel really extremely tired for no reason, felt like it was going away (was putting this on the stress of going back to school) and exactly 3 year's ago (in early 2016); BAM all of the PCS symptoms suddenly came back (migraines, sleeping problems, chronic fatigue & brain fog, etc...) exploded and I haven't been able to work since....

I tried to take a few meds that simply made me feel worse, so I started to take some CBD oil since a few months ago. It seems to help, but if there's a recovery, it's going on really slow. So, yeah, feels depressing but just to say that I understand how you feel and you are not alone living this.