1) Learn to suspend judgment. Science-y people tend towards authoritative, binary thinking; something is either wrong or right, someone either has these intentions or not. Maybe the person sort of hates you and on occasion, either willfully or subconsciously, does things to kind of dick you over. Maybe you subconsciously hate this person and are looking for "excuses" to place blame. You have to learn to leave things up in the air. Maybe they are gaslighting, so fucking what? Maybe you are forgetting things, so try and be more attentive. Many psychological disorders are a result of the mind imposing order that is not actually there.
2) Learn to say fuck it, but in a healthy way. Don't overthink it. Realize that the whole matter (worst case scenario) is just a result of some petty bitch's ego. Do you really care about some faggot's inter-office manipulations? Just do your work if you enjoy it. If it is too stressful and you can afford it, jump ship. But realize you will 99% regret it if you do.
3) Don't sink to the same games. People dick each other over. People can be manipulative. Don't give in to the pressure to get a competitive advantage by cheating life and being insincere or dishonest. Anyone who does isn't worth wasting energy over.
A full-on gaslighting campaign is rare, but the point is to not expend energy worrying about it. I have personally experienced the most hardcore black psych tactics from groups like scientology, and it doesn't amount to much when you put it in perspective. An individual or small group is not going to successfully gaslight anyone unless you are vulnerable already. An individual is not really gaslighting as much as being a dick. Most cases of gaslighting are figments of the imagination and can be overcome with good psychological hygiene (avoiding neurotic behavior, obsessive thought, compulsions). Successful gaslighting techniques are carried out by cults who control most aspects of a person's life already, not overly-sensitive faggots whose only strategy of conflict resolution is passive-aggressive manipulation. The thing that would fuck them in the ass the hardest would be if you just got better at your job and appeared more laid-back around the office.