There are many possible reasons why a cat may be acting weird and sluggish, including illness, stress, environmental changes, or a change in routine. If your cat is sick, they may show signs of lethargy, lack of appetite, and changes in behavior. If your cat is in pain, they may be reluctant to move or play, and may seem generally sluggish. If your cat is stressed or anxious, they may show changes in behavior, such as hiding or becoming aggressive, and may appear sluggish or lethargic. Changes in the home environment, such as a move or a new pet, can be stressful for cats and may cause them to act weird and sluggish. If there has been a change in your cat's routine, such as a change in feeding schedule or a change in who is caring for them, they may become stressed or anxious and act differently as a result. If you are concerned, it is always a good idea to take your cat to the vet for a check-up to rule out any underlying medical conditions.