Task: Classify the mental state of the tweeter based on the tweet, determining if it is 'neutral or no emotion' or characterized by any of the provided emotions (anger, anticipation, disgust, fear, joy, love, optimism, pessimism, sadness, surprise, trust).
Tweet: When you burst out crying alone and u realize that no one truly knows how unhappy you really are because you don't want anyone to know
This tweet contains emotions: 
sadness