43, left eye feels heavy vs. the right - why is this happening? (Photo)

You likely have asymmetric upper eyelid ptosis (and loose skin). See an oculoplastics expert for evaluation and treatment.

It appears that you have ptosis of your left upper eyelid. This condition occurs when a muscle in the upper eyelid becomes weakened and it allows the upper eyelid to fall lower across the eyeball than it should. Ptosis can normally be improved with a surgical procedure. I would consult with an oculoplastic surgeon or a surgeon experienced in ptosis repair surgery.

Droopy upper eyelid is a sign of a condition called eyelid ptosis. Correction is surgical. A consultation with a board certified plastic or oculoplastic surgeon is recommended. Good luck.

Seems like you have ptosis on one side and to compensate your frontal muscle is more active on left side and your eyebrow is higher. It is not possible to correctly diagnose the problem with only one photo, I'd recommend a consultation with a doctor.

You have some asymmetry of your orbits, and I believe your left orbital socket sits higher in your skull and may have a different shape compared to the right side.
Regardless you appear to have ptosis of both your upper eyelids and most likely this is causing some blocked peripheral vision.
Consider consulting with oculoplastic surgeons in your community or any type of plastic surgeon.
For eyelid issues, oculoplastic surgeons may have some advantage.
I do believe that skeletal structure is contributing significantly, though this probably does not explain your upper eyelid ptosis.
If your upper eyelids are blocking your peripheral vision, then medical insurance may cover surgery.
Best,
Mats Hagstrom MD