I suffered from health anxiety for a long time, and head sensations were the ones that got to me the most.
I've experienced every single symptom you described and more. If you look back on some of the posts I've made, you'll probably see that I've made posts on all of these symptoms at some point or another.
One of the symptoms that stuck with me the longest and effected me the most was the same 'gassy' feeling in the head. I described it as a 'slightly lightheaded, sort of dizzy sensation' that caused me to feel slightly unbalanced as you described. It stuck around with me for months and months, I went to the doctors for it 2 or 3 times and each time they said it was probably an inner-ear infection causing a sense of imbalance, but in hindsight, it was probably almost certainly just caused by excess adrenaline due to my anxiety/stress.
All of the symptoms you described and more can in-fact be caused by excess adrenaline due to anxiety/stress. Too much adrenaline can cause your vision to blur or make it hard to focus and it can make it hard to get a restful sleep which causes the constant tired feeling and heavy eyes.
I'm not a doctor, but as someone who has been in your situation and experienced every single one of the symptoms you describe, I can say that there is most likely nothing wrong with you and there's no reason to worry (and I know that is MUCH easier said than done).
Something that could help you is 'The Anxiety Guy' on YouTube, and in particular his 'Symptoms of Health Anxiety' videos. I think you'll quickly find that he describes every symptom you've listed above and that it was all caused by his health anxiety and nothing more. I'd also try to stay away from caffeine as much as possible because I've found that it only amplifies my symptoms and anxiety.
I'll find one of my old posts and post it here, have a read over it, I think you'll find that I describe what you're experiencing almost exactly and that it was all due to my anxiety and nothing more.
Good luck, and all the best.