Feelin' yourself refers to the state of having a sense of self-confidence. You are so pleased with the way you look that you would like to show it through everyday actions. What's more, you assume that others would think the same way.
A:"I look so good!"
wǒ kàn shàng qù měi jí le
B:"you need to chill. You are feelin' yourself way too much.
nǐ hái shì lěng jìng yí xià ba, nǐ zhè yě tài zì liàn le.
Source: China Daily