If trying to do just samatha practice or sitting at access concentration, it's important not to investigate and to just stay with the single chosen object of the meditation. Making resolves to stay at access concentration and not to enter (vipassana) jhana can help, as well as reducing sitting lengths. Sentences like this:
just kinda focusing on the feeling of quiet space in my head.
indicate too much investigation.
It's possible you were sitting in about first jhana territory, started inadvertently investigating and thus passed through mind and body, cause and effect, and into three characteristics and that is where the fear occurred. It's also possible you could have passed through the A&P and through dissolution and into the fear nana, but I think this is less likely without longer sitting periods for at least a couple days.
Feelings of spasms of energy firing off in my stomach and being able to watch mental images arise and then pass away in real-time
This could be strong mind and body, and not necessarily A&P.
Here is a quote by Daniel Ingram that might help:
First seeing the dot is the first samatha jhana, and in this case is the equivalent of Mind and Body, where mental phenomena become clear external objects. Noticing things about intention influencing the position and stability of the dot is cause and effect.
Shortly thereafter this would become irritating and the dot would begin to shake, shudder, split up, spin off to one side or the other, and generally seem to misbehave quite on its own. This was the entrance to the Three Characteristics.
So the point where your visual field turned vibratory could have been three characteristics and the three characteristics can be easily mistaken for the dark night.
So reduce your sitting lengths and make a resolve to not enter jhana when you sit (if this is even possible at this point), if you wish to avoid doing insight practices. Also, all your fears about not investigating while you're sitting may be causing you to investigate. Sort of like telling someone not to think about a "white elephant." Don't think about that white elephant! (and then someone immediately thinks of a white elephant). In this case, just stop practicing until the fear goes away. Don't let your fears become "self"-fulfilling prophecies!
EDIT: Also, try meditating with your eyes open instead of closed and see if that helps. This is to avoid inadvertent investigation of the flickering visual sensations.