Unexplained fainting is less serious and more common than you think.
www.nhs.uk/conditions/fainting/
Given you haven't been feeling well, I would focus on getting better, and if you don't faint again, it's probably just one of those things from having a bug. If you've never really fainted before, it can feel like a huge deal, but it's surprisingly normal.
If you faint again or feel worse, you need a GP appointment. Your GP can order blood tests to be taken to rule out any number of things.
You do sound disproportionately anxious - is it normal for you to worry this much? Is there anything else going on to make you feel so unsettled? Sometimes when we're dealing with worrying things, it makes everything seem scarier than it is.
For future reference, A&E is for anything life-threatening, plus serious injuries. Minor injuries can be treated at an urgent care centre, if you have one (they're usually attached to the A&E unit).
www.nhs.uk/nhs-services/urgent-and-emergency-care-services/when-to-go-to-ae/
If there is anything else wrong that isn't life-threatening or a serious injury, that's what your GP is for. An urgent care centre will x-ray a potentially broken foot that could get worse without being put in a cast there and then. If there's something a bit off, you're not sure what it is, and a lack of immediate answer is unlikely to affect your care, your GP practice will get blood tests done. That's the difference - it's in how quickly a medical professional has to react to ensure you don't come to harm.
It's important to go to the right place first time, as it will mean you will get the right care.
I hope you feel better soon, OP.