Welcome to the forum. It's not clear to me in your post that you have a definite diagnosis of dysautonomia. Have you seen a specialist? Have other causes of your symptoms been ruled out?
If this is dysautonomia--what works for me is increased salt, IV fluids, increased fluids in general, high potassium low sugar diet, small more frequent meals and more protein especially in the early part of the day. Also reducing external stimuli. When I am in a flare, even having the TV on can be too much. I need quiet space. I minimize looking at my phone, computer etc. Reading a book I can sometimes handle depending how symptomatic I am. Fresh air can be helpful, for me, as long as it isn't too hot out. Also I try not to lie down too much during the day bc for me lying down a lot just makes me eventually feel even worse when upright. As you mentioned, good rest/sleep at night is important. When I am in a flare my sleep can be very disrupted unfortunately.
I also take a beta blocker and increase the dose when symptomatic (advised by my dr). There are other medications that can be prescribed that can help.