Under the new privacy laws, the doctor CAN NOT release your Father-in-law's medical information to his son(s) unless he consents. The best way to ensure that the doctor has this consent on record is for the son(s) to go with him to a doctor's appointment as soon as possible, so the doctor can record the consent. Only the doctor can make a diagnosis of probable AD or another disease. It's possible that he has another dementia, has been having small strokes, is having a problem with his medications, etc. The symptoms that you describe do suggest that he should receive medical attention quickly since they appear to be consistent with Alzheimers (I'm not a doctor!). His living conditions may need to be monitored despite his claims to independence.
I do think that stress & changes can make an Alzheimer's patient more confused than usual. My husband definitely had set-backs with his Alzheimer's this Christmas.
The first two months after the diagnosis were the worst for us so far -- doing a lot of research, finding support services and learning how much help is out there has been a boost. Depending on your father-in-law's situation, the family may be able to obtain a housekeeper, home-health care, nursing home or assisted care, day-care services, etc. Some services are available through Medicare. Once you have identified the diagnosis, the next step will be to learn about the illness and to identify the level of care that he needs now (and that he will need in the months to come). You can find sources for this information from his doctor, or a local Alzheimer's or any elder-care group.
No matter what the diagnosis, it's time for the family to take care of business. Putting a living will, durable power of attorney and testamentary will in place are good ideas for everyone -- I did mine when we put these documents in place for my husband after he was diagnosed with early onset Alzheimer's. At 82, your father-in-law may already have taken care of this? If not, whoever prepares the documents will need to be sure that your father-in-law still has the capacity to understand their legal effect. If he does not have this capacity any longer, it may be necessary to have a Guardian appointed for him (a longer and more expensive legal process that will involve your local Surrogate/Probate Court). Split between the sons, you may be looking at a cost of $150 or less for an initial consultation with an elder-care specialist. Keep in mind that everyone will have different interests, and the attorney will need to know who he is representing. The family's children typically are concerned about their parent's care but also with trying to preserve whatever estate remains, and the parent may be more concerned with retaining control of their hard-earned property. I don't mean to dwell on this stuff when your're just worried about getting a diagnosis, but your visit to a lawyer can be more efficient if the family has given some of these issues some thought beforehand.
People on these boards are very kind and helpful. Keep in mind, though, that posters can only give information based on our own experiences or research. Medical suggestions should be taken to your father-in-law's doctor. There are no black & white answers that will apply to every family -- our family is dealing with an employed father of minor children, for example, so the benefits available to us from Social Security will be completely different from the benefits available to an 82-year old patient. Recommendations for a patient in the early stages of Alzheimers who is still legally competent & able to take care of himself/herself will be very different from the issues presented by a mid- or late- stage Alzheimer's patient.
First step -- get your medical diagnosis. Our prayers are with your family & your father-in-law.