Small correction, but this bit isn't quite correct:
If you go just below light speed, you’ll see the world outside go past like it’s being fast forwarded, and when you return, 8 years will have been compressed into something that seems much shorter to you.
During the time that you are just below light speed at a constant velocity, clocks that are "stationary" will appear to be moving slow to you. And clocks moving with you will appear to be running slow for a "stationary" observer. As I mentioned in a comment in another reply, the trip would feel short to you because the distance to your destination would contract to nearly zero. "Fast forwarding" (ie, having both you and a stationary observer agree that more time has passed on the stationary observer's clock) would happen during the periods of acceleration/deceleration at the beginning and end of the trip.
HIPAA allows medical care providers to share your information with each other for the purposes of providing care (whether that sharing happens through MyChart or some other means). It does not require your consent (and this could be a good thing if, for example, you were taken to a hospital while unconscious). You simply may not have a lot of options for preventing this. As NOT_RICK mentioned, you could opt out of Care Everywhere at the psychiatric hospital to prevent them from sharing your information that way. You could also try to amend their record or request that they restrict access to your records, as per https://www.hhs.gov/hipaa/for-professionals/privacy/laws-regulations/index.html#general. All of those options would require interacting with the original psychiatric hospital, so if you're unwilling to do that, I'm not aware that there are other options available.