Hi and welcome,
The way you've described this began would usually be suggestive-consistent with a typical nerve impingement-entrapment cause and effect situation, the cause would be the bent positioning of your shoulder-elbow-wrist whilst driving and the effect would be temporary nerve entrapment sign of tingling- pins and needles eg ulnar nerve entrapment whilst driving commonly occurs after the ulnar nerve in the elbow has been compressed. There is something specific to driving it's called 'drivers elbow', which is when the is shoulder is held away from the torso (abducted) and the elbow is also bent (flexed), think of the typical position of the arm lying against the lower edge of the window whilst driving...
You said "my left leg started to feel heavy a day or two after and then the rest of the left side of my body followed suit. If you draw a line down my body, the entire left side just feels heavy and “disconnected” from my right" ......."I started to get muscle twitches throughout my body and they’re literally everywhere. The twitches usually occur when I’m laying down or not moving"
Feeling like some parts of your body are 'disconnected and heavy' along with random all over 'muscle twitching' when inactive and feeling more tired, sleepy or fatigued are not uncommon experiences with some types of mental health conditions eg anxiety, conversion disorder, depersonalization/derealization disorder etc.....so a mental health causation is possible, i'm not saying it is the causation just that it is a potential causation.
The potential of a mental health causation would increase into being a more likely cause than a neurological cause 'IF' all your related test results, including your neurological clinical signs are not actually abnormal....Sometimes the difference a person feels is not a clinically true neurological abnormality from disease or damage to the nervous system but a problem with the perception of an abnormality, it can feel the same but the causation and treatment plan is vastly different.
"There’s some muscles in my leg I can’t flex as hard as the ones on my right. My face is the same way along with my arm."....Keep in mind that it is perfectly normal to have asymmetrical muscle flex, strength, size etc, if you are right handed it's usually the right side of your body that is your stronger and more dominant side and the muscle development will be slightly smaller, weaker etc on your left side, the left side not flexing like the right is a common discussion topic on body building and gym sites.
You have about a month before your neurological appointment is scheduled and if your doctor has suggested it might be mental health related (anxiety), it would be in your best interest to get a psychological assessment done by a psychiatrist or psychologist before seeing the neurologist so you can already have a mental health causation taken off your possible causes list. It will also really help to have the additional support if your finding your anxiety is escalating to high and your starting to freak out....
I hope that helps.........JJ