Gaslighting is another form of bullying and the gaslighter is likely trying to get one up on you from their own warped sense of their story. It can of course make you feel like you are losing your marbles and your self-worth will take a bashing and that is ultimately what the gaslighter wants, you to be perceived as weaker than them and to be weaker than them.
You will see the pattern of power over emerging as you start to look at your individual relationship dynamic.