Those symptoms sound consistent with exactly what one might expect from withdrawal from an SNRI (Serotonin and Norepinephrine Reuptake Inhibitor), which Pristiq is. The brain zaps, loss of balance, and irritability are all considered common. Additionally, doctors often prescribe a benzodiazepine like Valium, Xanax, etc to counteract the side effects.
If you experience anything more severe you should contact your prescribing physician, but from what you've described, it is consistent with normal withdrawal from the Pristiq.
Thank you for the further questions - that helps me to address the issue.
First off, the withdrawal from an SNRI can last anywhere from 2 weeks to several months. Since you were on the Pristiq for several years, the withdrawal could last a while. The way in which you are withdrawing sounds fine - usually a taper is done down to the lowest amount (from 200 to 50mg in your case). Then the pills are taken every other day, then every third day, etc. The Valium can be taken to counteract the effects, but it should only be taken as needed. If you need it to sleep, then taking it at night is recommended. Increasing the dose or taking it for longer than you need to isn't wise as it can cause dependence (benzodiazepines are very addictive).
You mentioned being addicted to the Pristiq - and you are correct. In some ways, your body is addicted to it because it needs the drug to feel "normal" - just like someone who is trying to get off of cigarettes. In that sense, taking one will get rid of the side effects. However, it's just a temporary fix. Unless you are experiencing intolerable side effects, introducing more into your system will just encourage the cycle to go on. The best way would be to call your prescribing physician.