Mythomania is a condition where someone has a strong need to tell lies and make up stories.
Mythomania is a serious thing and can make people not trust the person who has it.
Examples:
Mythomania makes people tell lies all the time.
She has mythomania, so we can't believe what she says.
His mythomania makes it hard for people to trust him.
Mythomania is like a never-ending story machine!
Her mythomania is so bad, she even lies about what she had for breakfast.
Mythomania can make people feel very sad and alone.