On swelling and time:

Sensitivity to certain alkaloids naturally present in “nightshade” vegetables causes pain and swelling in a significant minority of individuals with degenerative arthritis. Nightshade sensitivity is not the same as allergy, and is not detectable by any laboratory tests in current use. The only way to figure out whether nightshade vegetables bother you is to totally eliminate tomatoes, potatoes, peppers, and eggplant from your diet, along with tobacco exposure in any form. Even if you’re nightshade sensitive and totally eliminate all of these, it can still take three to four months for symptoms to recede.

from Tahoma Clinic on Degenerative Arthritis

On what plants are included and doctor reactions to discussions of nightshade allergies and attendant problems:

the Fijian headhunter Cannibal Tomato or the Tasmanian Kangaroo Apple, not to mention the tasty tropical Zombi Apple.

These exotic fruits, along with his familiar favorites of tomato, potato, peppers, and eggplant are all members of a class of plants called the Nightshades (named after the Deadly Nightshade plant), to which he had apparently developed a sensitivity. The botanical family known as Solanaceae, also contains a number of poisonous and hallucinogenic plants, as well as medicinal herbs, some of which are used to manufacture commonly prescribed medications, such as atropine and belladonna.
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Some patients claim that certain foods cause them a host of more ill-defined symptoms, like fatigue, irritability, muscle pains, hyperactivity, or depression. These peculiar reactions are labeled “food idiosyncrasy”. Patients with food idiosyncrasies are often felt by their doctors to have “Prozac Deficiency Disease”, and may even be referred to a mental health professional for evaluation, as their symptoms can be rather bizarre and difficult to relate to food ingestion.

from Killer Ketchup

Subtle food allergies, that attack physically, emotionally, or mentally, along with time frame for symptoms:

Most people are familiar with the kind of food allergies that make you swell up or break out. These obvious “violent reaction” allergies are caused by a single food like Shellfish or Peanuts. However, it’s estimated that up to 50% of Americans suffer from more subtle food allergies, or sensitivities. More difficult to pinpoint, these allergies don’t immediately make you puff up like a blowfish or break out in horrible hives. Hidden food allergies affedt your quality of life in more insidious ways: physically, emotionally,and mentally. Symptoms are highly individualized, including a muddled brain, mysterious diarrhea, or multiple ailments. Some symptoms do not appear until 3 days after eating an allergic food.

What Causes Hidden Food Allergies?

Essentially, a body out of balance: any single food can upset your body’s delicate mineral balance, and then start a chain reaction that impairs your digestion and immune ystem. One of the biggest culprits may be the Standard American Diet (SAD). Refined flour, white sugar, and processed foods are new inventions that don’t come with the minerals we need to spark digestion. SAD also centers on only a few foods like beef, eggs, dairy products, wheat, corn, and sugar. We unwittingly eat these foods every day – yet many of us are allergic or sensitive to them. These foods damage our tissues and our bodies need 3 to 4 days between eating allergic foods to recover.

How Can I Be Allergic To Food?

When you have a food allergy, your immune system is responding improperly to a substance that is not usually harmful. Of course, wholesome food is not innately bad. Yet, even good foods can turn bad in a body out of balance.

from GeoCities, Food Sensitivity and Allergies

Foods such as potatoes, tomatoes and eggplant sometimes referred to as “nightshade foods” could be the cause of stiff joints, pain and inflammation.

from Arthritis Support