For budgerigars -- or parakeets -- symptoms of a seizure or stroke are similar. No matter which one your pet is experiencing, it's an emergency requiring immediate veterinary attention. Stroke, also known as cerebral apoplexy, occurs far less often. Budgies experiencing strokes are generally elderly -- at least 5 years old.
If your bird displays any sort of neurological problem, it could have been a result of a stroke or seizure. You might find him on the bottom of the cage, appearing disoriented and unable to right himself. He could lose control of his bowels and make odd noises. Your veterinarian must make a diagnosis. If your bird suffered a stroke, the prognosis usually isn't good. If it's a seizure, medication and dietary changes might help your pet.
Your budgie is far more likely to suffer from heat stroke than a cerebral stroke, especially if he is overweight. Parakeets are sensitive to temperature changes. In hot weather, affected birds pant, experience difficulty balancing and hold their wings out. Call your vet, but relocate your bird to a cooler area and mist him gently with cool -- not cold -- water. (ref 3)