nicoleoops you told me that something I know in my head isn't true, when things in my head are the only things I can be 100% sure are true-- I don't know you exist 100% but I know what's in my head is some form of experience being experienced by something
obviously you can go too far with this-- if you, say, hear a voice in your head, the fact that you hear the voice is something you know happened, but it doesn't mean the voice corresponds with something in external reality or that the voice is telling you something worth listening to
but you know you had the experience! if someone said "you did not have that experience" you know they are wrong