Why does my parakeet (budgie) suddenly freeze? Is it normal?

Many birds, including budgies, will sleep with their heads nestled down over their backs and between their wings, especially at night. This is perfectly normal behavior. However, a bird that isn't feeling well will spend more time with its heads nestled down into its feathers and less time engaging in preening, eating, playing, and other normal activities. A sick bird may also stop vocalizing, sit puffed or fluffed up, sneeze or have discharge from their nares, have loose stools, have stools caked around the vent, and/or pick at its food or not eat at all. So, if your bird seems listless or is exhibiting any of the above symptoms, seek veterinary attention right away.

It's possible something may have startled your bird and is causing the wary behavior you are seeing, however if she is puffed up or refusing to eat/drink then that can indicate a potential illness. If you see other signs such as changes to the stool, or listless behavior those can also indicate illness and should be checked out by a vet. Otherwise, giving her a little space and leaving food and water where she can easily access it may help her calm down some and return to normal behavior.

That just sounds like a relaxation behavior or possibly adjusting the food in her crop, and is very normal. As long as Juno is otherwise healthy, active, and happy, I would not be too concerned. If she shows any signs of illness in addition to this, seems in distress, or does it constantly without stopping, seeking a vet exam in person is always best.

A sudden behavioral change can sometimes indicate a health issue that is underlying, so a good first step is always to schedule a vet checkup and rule out any health issues. If Banana checks out healthy, looking to things that could have changed (new neighbor with a loud car? New pet? People in the house visiting) may help you clue into why he is having a behavioral change. Adding in some toys that can distract him or that he can snuggle with may help, as well as offering a treat every time you interact to help him relax. In some cases, sexual maturity may cause behavioral changes (though this usually involves lashing out rather than hiding/being fearful.) Lowering the amount of protein in his diet and decreasing daylight hours may however help if the change is hormonal related.

Tail bobbing isn't really a symptom in itself, unless you are seeing other signs such as difficulty breathing, sleeping all the time, not eating/drinking. It could be you are just startling your birds, so they are hunching down when you are near, or they are just active and moving about if they otherwise seem healthy. Offering a treat when you come by to visit can help them bond with you. If you do start seeing any signs of illness, or respiratory distress (heavy breathing, panting, etc) then scheduling a vet visit to rule out any more serious issue is best.

It might be that he's not actually completely asleep, or he's just having a good dream! If he's otherwise healthy, active and normal, I wouldn't be too concerned. However, if you are seeing any signs of illness while he is awake such as lethargy, puffed feathers, not wanting to eat or drink, trouble breathing, etc, then this may be a sign there is something underlying which should be checked out by a vet.

It's possible Sharpie may have just been stretching oddly, however if you continue to see odd or jerking movements, she doesn't perk back up, or you see new signs of illness such as refusal to eat or drink, it is best to schedule a veterinary exam. Neurologic issues, illness, and toxicity may all cause strange random movements or jerking motion in addition to other symptoms.