I worked in health and safety. One of the things we had to monitor was lead.
Lead almost always gets into the body through the mouth.
Things like zinc can be very harmful as "fumes, lead can be also. This happens when someone welds or cuts with a torch.
This is called "metal fume fever" and is quite striking and can make you very sick for a short time. Again this is with usually cutting or welding. Solder temperatures are not that high.
Lead poisoning happens almost always through the mouth. Grinding used to be a common cause of lead poisoning in auto body production when lead was used to cover seams in auto bodies. The lead was applied in semi solid form at controlled temperatures with such implements as putty knives and then ground down with powered grinders. Talk about a good (bad?) way to get particles airborne and into your face!!! This has been eliminated in production as far as I know. This method of auto body repair also resulted in the term "lead sled" i.e. a custom auto body. Almost impossible to find anyone who is skilled enough to do this.
Another place where lead exposure can be high is in lead battery recycling where old batteries are crushed and lead separated by physical methods before being re smelted. Also lead smelting and refining.
We had one goofy guy who had high lead levels. Turns out he had a habit of keeping bullets in his pocket (I do not know why), bullet to hand to mouth. I just bring this up to emphasize the oral rout. This would also go to old toy lead soldiers and old toys painted in lead paint.
Lead levels decreased in workers when proper industrial hygiene was implemented. The most effective procedures for safety included bans on eating, drinking and smoking when there was lead dust involved. Also there were facilities available for showering and for containment of work clothing so lead would not follow workers home.
Slag from the top of molten lead pots is dangerous also. It can become airborne as dust much more easily than molten lead. This is dust,not "fumes", but a bad source of lead exposure.
Childhood lead poising is mostly from eating lead paint which tasted pretty good. Another source is water. There are thousands of miles of lead pipes carrying city water to millions of homes last that I knew. (Remember Flint, Michigan??) This can be a problem if the water is acidic, then the lead leaches from the pipes and into the water. Some pewter serving vessels and some ceramic glazes contained lead. Do not drink tomato juice or lemonade from these . These vessels are an unlikely source of lead poisoning. I do not think they make these things anymore but there are some old ones about and who knows what amateur potters will use?
As far as "flux" goes... It is variable. There are many "fluxes" one of the predominant fluxes in the past was Rosin, a pine tree product used in lots of things including shoe manufacturing and the bag at pitcher's mound. It can be an allergen. Some people are allergic to it and get allergic rashes.
Multiple studies have shown no risk to solderers in electronic assembly in the past where soldering was done by hand. This was done in assembly where workers soldered 8 hours a day. But again proper hygiene and eliminating oral rout of contamination by little particles of lead is necessary.
Here is my opinion:
Solder fume extractors probably do not meet any standards but cannot hurt. They just take some smoke particles out of the air. Good idea but no where near getting most of the particles out of the air. Can't hurt.
Proper hygiene should focus on hand to mouth contamination with lead. Lead will rub off on your fingers just by handling cold solder, Just look at you fingers after an hour or so of soldering.
There were people who were advertising "chelation" as a treatment for undiagnosed chronic heavy metal poisoning(all sorts of heavy metals, not just lead). Chelation is extremely dangerous and can kill you.
As to the "allergic" reaction described as being "foggy", pardon me if this offends you, that is not my intention. These "unusual" symptoms have been described in connection to all sorts of things, one of them is chocolate.(believe it or not).
I really do not know if these things are really connected to the alleged "allergen" but there are some boni fide real allergists (MDs) who believe it. Things like this are an ongoing topic and I reserve my right to have no opinion except to again say there are some very conservative good allergists who believe in these allergic connections.(maybe "allergic" is the wrong term here maybe "idiosyncratic" to include non allergic reactions?) If this is the case that there is some sort of individual reaction, I would doubt that a standard solder fume filter would eliminate the exposure.
Allergies like "hay fever", (really ragweed or Russian ragweed, i.e tumbleweed) do make people sleepy besides making them miserable. I know, I have hay fever.
Wally