Simply put, gaslighting is a technique that someone uses that can make you question your perception of reality. It is a form of psychological abuse whether the person intends to do this consciously or unconsciously. As a result, you can leave a conversation second guessing yourself and how you feel. They may say things like, "you're so insensitive," or "it's not that big of a deal," or "how could you think such a thing."
If you have experienced being gaslit, remember that you're not being too sensitive, and that more than likely you've just not felt seen, heard or understood. Remind yourself that you're not overreacting but that more than likely you've been triggered by a wound or a past trauma.