Task: Identify the primary emotion conveyed in the tweet and assign it to either 'neutral or no emotion' or one or more of the provided emotions (anger, anticipation, disgust, fear, joy, love, optimism, pessimism, sadness, surprise, trust) that best capture the tweeter's mental state.
Tweet: I feel ghastly and I'm really hoping it's just a post-birthday slump. Back to full research mode tomorrow either way.
This tweet contains emotions: 
anticipation, disgust, fear, optimism, sadness