Antonyms for the phrase "top form" would be words that describe a state of being below average or performing poorly physically or mentally. These could include words such as "subpar," "mediocre," "out of shape," "out of sorts," "below par," "sluggish," "lethargic," "unenergetic," "unfit," or "unwell." When someone is not in top form, they may lack motivation or drive, exhibit signs of fatigue or illness, or simply not be performing at their best. It's important to acknowledge that we all experience fluctuations in our mental and physical states, and that it's okay to not always be at our absolute best.