I have a theory that the emojis you use are indicative of your habits and mood. Maybe you don't use emojis, which is telling in itself. If you do use emojis, take a moment and look at your favorite messaging app to see your "Frequently Used" emoji's. I know iPhones have this feature in the Messages app. I have no idea about Android so you all are on your own.
One friend of mine pointed out that the "Frequently Used" section includes an emoji he has only used one time the previous day. So, I suppose this area is for both frequent and recent emojis. Nevertheless, the distinction is not important for this exercise.
Take a look at your emojis in this section. Are they mainly objects? Faces and body parts? For the ones tied to emotions, how many represent positive emotions? Negative ones? Reviewing emojis in this way provides a quick "hack" to gauge your emotions over a recent period of time.
I wonder if there are any studies about emojis. Maybe there would be a bias toward positive emojis since when you are agitated or angry you may not be inclined to use them.
Are you happy with what you saw? Remember, what you focus on expands. This list of emojis is a small sample of the ideas and thoughts and feelings you have been communicating. Repeat this exercise as frequently as needed to assess your mental/emotional state.
I just had an idea for an app. The app scrapes the emoji data from the Messages app (if apps are allowed to read that data) and then summarizes the data to show you frequency by day and even person. Again Android, you're on your own. I wonder if people would find these data useful?