Barometric pressure, temperature, moon phase?

Remove your hat.

I agree w/elizabeth could be sinus/middle ear related.  Since I was 30-something I have had allergies year-round where I live (tree and grass pollen) and it definitely affects hearing.  I take Loratadine daily and it seems to help.

Perceptions are NOT reality. They are just perceptions.

Perception IS reality. Our sensory perceptions are precisely how we observe reality. The word perception can sometimes be used as a psychological term, but it’s actually not. It’s the same thing as hearing. There’s no difference.

Be it sight, sound, the smell, the touch.
There's something,
Inside that we need so much,
The sight of a touch, or the scent of a sound,Or the strength of an arquebus deep in the ground.
The wonder of flowers, to be covered, and then to burst up,
through tarmack, to the sun again,
Or to fly to the sun without burning a wing,To lie in the meadow and hear the grass sing,
To have all these things in our memories hoard,
And to use them,
To help us,To find...

@dprincipato
You may find http://ielogical.com/Audio/WinterBlues.php interesting and specifically http://ielogical.com/Audio/WinterBlues.php#TheFly for the effect of temperature on speaker XOver

You did not mention the source. LP playback systems are subject to all manner of temperature related foibles: bearing tolerance, lubrication viscosity, cantilever suspension compliance, vinyl plasticity.

Do you note levels at which you play a particular piece?
How repeatable is your level control?

When mixing, we calibrated the playback level to the speakers to ±0.1db. The room was temperature controlled to ±1.0°F. When we were satisfied, we always checked the next day on cold monitors. Mixes made in the heat of summer sounded different even though the room temperature was nearly identical as rooms were not humidity controlled. Line voltage and dirt varies considerably in Los Angeles, so we recorded and mixed late a night when the vagaries were minimized.