Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
I would be happy to provide you with information about Bell's Palsy.
There are 12 nerves, called cranial nerves, that supply our face. One of these nerves is called the 7th cranial nerve, of facial nerve. It innervates several parts of the face, including the muscles we use for facial expression (smiling, closing the eyes, looking surprised). It also has such functions as helping us perceive taste on part of our tongue, and dampens sounds so that they are not too loud. It is also involved in our eyes tearing and in our mouth watering.
Bell's Palsy (named after the physician who discovered it) is a condition that results from a lack of function of the facial nerve, and the problem leading to this dysfunction can be anywhere from the origin of the nerve to anywhere in its path where it gives of smaller nerves to supply all the areas described above.
Weakness of an entire side of the face (including the forehead, eye, cheek, and neck muscles) occurs. A person with Bell's palsy is unable to raise up their forehead, close their eye, smile, or contract their neck muscle on the affected side.
Many patients complain of sensory symptoms such as numbness or tingling in the face on the same side of the weakness. Where the lesion is determines what additional symptoms there are. If the lesion is close to the origin of the nerve, then in addition to complete weakness of the face (on the same side of the affected nerve), symptoms will include lack of tearing from the eye on the same side. If the lesion involves the nerve prior to where it branches off to the tongue, taste may be involved. And so on.
It could be "idiopathic", meaning having no known, identifiable cause, or secondary to other processes, including but not limited to infections (such as Lyme disease or Herpes infection) or inflammation (such as in the condition called sarcoidosis). If it is isolated, meaning that no other findings are present, then it is highly unlikely to be due to a stroke, tumor, or other causes. However, if for example, the body on the side opposite of the facial weakness is also weak, the latter causes need to be ruled out.
A recent study showed that treatment with a type of steroid called prednisone for 10 days helps the nerve recover function. Until the eye can be closed properly, natural tears and ointment should be applied to the eye to protect it.
The extent of recovery will depend on the cause, and the age of the patient. In idiopathic cases in younger individuals, complete or near complete recovery of the function of the facial nerve over weeks to 2-3 months is expected. In some cases, there is partial recovery, and much less commonly, there is little recovery of function.
Thank you for this opportunity to answer your questions, good luck.