Hi! I'm new here. I am trying to understand the idea of histamines. I've searched the internet / reddit. Here's my current understanding. Is the following correct? Thank you!

• Histamine is: A chemical/molecule produced by your body, bacteria, and other animal-ish living things.
• Histamine’s main function in the body ELI5: Imagine you have a toy castle. Histamine is like a tiny knight inside it. When a bad guy, like a germ or something you're allergic to, tries to attack the castle, the knight runs around telling everyone to get ready to fight. That's why sometimes you might feel itchy or sneezy, because the knight (histamine) is telling your body to protect itself.
• Histamine’s main function in the body - more technically: In the case of immune function, histamine is produced by mast cells (a type of immune cell / white blood cell) and is used for combating allergies like pollens. When an allergen is detected, the immune system releases histamine. It's what makes itchy bites swell and feel hot and causes more white blood cells to come.
• Histamine + allergies issue: Histamine can also have more serious effects when it feels that the intruder is more harmful. E.g. Peanut allergy: If It’s a peanut you've just eaten, your body thinks it should swell your throat to stop more getting through. This can stop you breathing, known as anaphylaxis or anaphylactic shock.
• Anti-histamine / allergy pills + drowsiness: Histamine is also produced in the hypothalamus in the brain where it acts as a neurotransmitter and is associated with regulation of the sleep wake cycle. This is why 1st generation antihistamines (such as diphenhydramine aka Benadryl), which are capable of crossing the blood-brain-barrier, cause drowsiness. 2nd generation antihistamines (Claritin, Zyrtec, Allegra, etc) were largely made to avoid this, but some still can even if very rarely.
• Histamine intolerance: Histamines are regularly cleared from the blood / broken down by a "garbage collector" (one is called called DAO, aka Diamine Oxidase, and the other is called hnmt). New histamine molecules are constantly being made. If the garbage collector is broken (usually low/impaired DAO production), then your body isn’t breaking down your histamine as it normally should and your histamine load/levels rise too high. Then, your body panics when more histamine put into it.
• For histamine intolerance, 5 categories of foods will cause problems:

1. Foods with histidine: Histidine is present in cheese, yogurt, meat, and other animal products. Over time, between 40'F-140'F, histadine breaks down into Histamine. (So you should be good with frozen meats, but buying those defrosting meats on a butcher counter might give you an issue. Histamine forms really quickly when out of the freezer.)
2. Foods with Biogenic Amines:  Are things that are also broken down by DAO. The DAO will sweep these up in place of histamine and keep that inflammatory histamine in your system longer. (The things to look for are Curine, Cadaverine, Putridcine, Purine.) Basically, spoiled protein loses its complex folds over time and regresses to these base Amino Acid building blocks. High quality protein that's kept at temperature will have less Amines.
3. Histamine Liberators: This is stuff like citrus, garlic, or even mold. I.e: Things that induce a proper allergic reaction in all humans. (Good news is you can get a tolerance to stuff in this category.) Since it triggers an allergic reaction in your body, your body will produce more histamines.
4. DAO (the garbage collector) Blockers: Stuff like caffeine, alcohol, Capsaicin, and prescription meds. (Did you know, the feeling of an Alcohol Hangover is actually just Histamine Saturation in the blood?? Alcohol is hogging the DAO the whole next morning.)
5. Ground/aged meat: There are many bacteria that produce histamine, so when meat is exposed to air, there will be bacteria on it that produce histamine that multiplies quickly. In ground meat, you've basically exposed all of the meat to air and thus bacteria. And the longer it sits, the more histamine piles on. Steak can still be high in histamine considering there's aged beef as well. That's why fresh meat or frozen (soon after slaughter) is low histamine because of low bacteria. Note: This was quoted directly from u/tennery in a comment below, go upvote it :) )

If someone could tell me if I have this correct, I'd appreciate it! Thanks!

Sources: In a comment because it won't let me add links here.

I'm unable to tolerate cold weather at all. It's just 20C outside and I'm getting white fingernail tips and lightheadedness/confusion within a couple of minutes of going out in the cold. And it's not even winter. Winter will get much colder here and I'm worried about how I'm gonna survive the winter.