I think you have most likely badly bruised your rib cage
. This can cause the degree of pain you describe. The concern would be that you may have fractured ribs but this is probably not the case with a fall onto a chair.
I would suggest you take paracetamol
for the pain and wait 2 to 3 days. if the pain does not improve then a visit to your emergency department would be appropriate.
Dr K A Pottinger,