Hi Monica_dr,
sorry to hear that vaping has been giving you a bad time. I hope that if you want to use vaping to get off and stay off the smokes, that you can figure out what works for you.
I know that for me, in 6 months of vaping and free of the smokes, I've had a range of issues, some may be vaping related, some were (or are) a result of quitting smoking.
The first thing that I was able to figure out is that I got more anxiety and mild depression when I quit smoking, but more noticeably when I went from my 18mg strength juice down to 12 and 9mg juices. At first I thought everything was fine, but looking back, my increased anxiety started when I dropped the nic strength. At the moment I am back on my 18mg juice, and I feel much better again. I also have had dizzy spells as well, not as bad as you describe, but a number of times I have felt a bit unsteady for a few seconds, mostly when changing position. For me, this could be anxiety related, or perhaps blood-pressure related, or maybe my body is still getting used to oxygen

, having been starved of it all those years I was a smoker. Ironically, when I was a smoker, my blood pressure was reliably 120/80; but the first time I had a reading since off the smokes, it was closer to 150. My Dr. thinks it is a result of the higher anxiety I was feeling at the time. Whilst conventional wisdom says that quitting smoking should lower blood pressure, there are tons of reports of people who experienced higher than normal blood pressure after quitting smoking.
As othes have said, if you can, try experimenting with 0 nic vs higher nic, and try 100% VG, then 100% PG, all one by one, and see if you are able to reliably nail down any (or none) of these as the cause. The difficulty is being able to identify what is vaping related (if at all), what is a result of not smoking (if at all), and then what might be another cause.
In my journey I have been able to identify that high or max VG liquids tend to upset my stomach more, with associated trips to the "local throne room". Also, as much as I wanted to cut the nic strength down, for now I have decided that I'd rather just vape 18mg and not feel anxiety and depression. For me (and I am not saying this is true for you), when I was in more extreme states of anxiety from getting less nicotine, I noticed that any body feelings, pains or symtoms I was feeling were greatly magnified. For you, if you are sub-ohming, you might be getting a lot
more nicotine. As other have suggested, maybe go back to a mouth to lung kit at higher Ohms. That way you'd get less nicotine, but could still have the vape-to-mouth behaviour and pleasure, closer to smoking behaviour.
Hope that helps, and please let us know how you get on.