These sound like panic attacks, which are very common and very treatable. Before assuming that is the cause of her symptoms, however, she should see her physician and be sure
there is not some other medical explanation. One of the medical explanations to consider if she experiences the hallucinations before the anxiety hits, is that the hallucinations may be the primary problem. It is common with Parkinson's Disease to have hallucinations either because of the disease itself, or because of the medications used to treat the disease. The medications used to treat Parkinson's Disease are meant primarily to increase dopamine, and while that helps with the rigidity, tremor and slow movements, it can cause hallucinations. This can be treated by either reducing the medications that increase dopamine, or by adding an antipsychotic medication.
If there is not another medical explanation for her symptoms, she probably is dealing with panic attacks. Panic attacks are characterized by the sudden onset of severe anxiety, which is associated with a number of physiologic symptoms. The anxiety goes from 0 to 100 in what feels like no time, and generally the person experiences palpitations and sweating along with the intense anxiety. Other common symptoms include trembling, shortness of breath, chest pain, dizziness, fear of going crazy or dying, and a tingling sensation. It is common to feel as though everything is foggy and unreal or feel detached, as though mind and body are disconnected. Actual hallucinations are less common.
The treatment for someone who is having multiple panic attacks is a combination of talk therapy and antidepressant medication. The talk therapy is primarily education about the illness, which we know is a physiological problem, and help with relaxation exercises to use at the start of a panic attack. Antidepressants are very helpful in preventing these attacks. It is very common that someone who has panic attacks will try to self-medicate with alcohol. This will decrease the anxiety that people often experience as they worry about having more of these frightening attacks, but it will not prevent the attacks themselves, and may even increase the risk of such attacks. Panic attacks are extremely uncomfortable, and it is very important therefore that your mother-in-law get proper care.