Dramatic increase in symptoms.
 

Hello,

This morning I went to the grocery store to get fruit and yogurt. After leaving, I got into my car, turned it on, and stalled the hell out of it. It's a manual transmission and I had forgotten that I left it parked in gear. The force of the car lurching forward sent my head back abruptly.

When I got home I went straight to sleep. Now awake, I feel in a daze, with many other symptoms returning, and still sleepy, which is unusual of late. I can't imagine this concussing someone with an uninjured brain. Whiplash maybe. But could this be a new head injury? I'm admittedly worried about the returning symptoms, which isn't helping.
If this is just back or neck related, is there any reason to wait before seeking some sort of treatment?

Also, this is the 2nd time i've stalled a car. The other time a few weeks ago, I didn't notice any increase in symptoms, besides neck soreness.

No, that was not a concussion or other traumatic force to your head. You may have strained your neck very mildly. Ice it if it feels stiff. This is again a startle response/anxiety issue. It startled you and annoyed you and may have even made you mad. When you add "Did I concuss my brain?" , you only make it worse.

I think you're right, it's probably anxiety. I've been trying my best to stay calm. I just get so freaked out, especially when symptoms ease for a couple of weeks, and then something else happens. But going to try to relax and ice.

Relaxing is great but you need to convince yourself that these bumps and jolts are meaningless. These bumps and jolts will continue to happen. You can not stop them. You can only control how you respond. Plan for the best and accept what happens and move on.