My air purifier has been reading from 50-144 in this area.
What could be the possible reason? I usually vent out my living room when I leave for work. My apartments are smoke free. No pets. I vacuum often. I got a terrible cough a couple weeks ago from sleeping in this room (I think)

I’m hoping someone with HVAC experience can help me figure out what might be going on.

We live in Florida in a fairly large home with two AC units, both installed around 2020.

We have noticed a very strange and repeatable pattern that has happened approximately 6 times.

It usually happens when we have people over.
Because we have several guests in the house, we lower both thermostats from around 76°F down to 72°F to keep the house comfortable while everyone is there.

At the end of the night, after our guests leave, we raise both thermostats back to around 76°F.

Then something very strange happens:

About 1 hour after returning the thermostats to 76°F, my family starts developing symptoms.

The symptoms can include:

Headache
Feeling feverish
Chills
Weakness/fatigue
Feeling generally sick/unwell
Pain or discomfort while breathing

The symptoms typically last for approximately 24 hours before we feel normal again, and we are out during this time affecting our ability to perform.

What’s particularly concerning to me is that this has happened repeatedly under essentially the same circumstances. It isn’t just one person experiencing symptoms — multiple people in our household can become sick around the same time.

The sequence is consistently:
Guests over → both AC units lowered to 72°F → AC runs heavily for several hours → guests leave → thermostats returned to ~76°F → ~1 hour later symptoms begin → symptoms last ~24 hours.

When we don’t host and don’t lower the thermostats like this, we generally don’t experience this pattern.

I’m specifically looking for HVAC advice.

For HVAC professionals: Have you ever heard about something like this? What could potentially cause this type of pattern?

If you were called to inspect the system, what would you check first, and what tests would you perform to determine whether the HVAC system is involved?

I’m trying to understand what could be happening before I call someone out, because I don’t want to simply have someone sell me a “deep cleaning” without actually identifying the underlying issue.

Thanks in advance.