@Hit I did similiar to you finally had the energy to garden and then my shoulder hurt the next couple of days.
I cant blame my problem on gardening but developed a motor cuff shoulder injury shortly after. Many months on I am healing. My injury happened straight after radiation and the suggestion was having my arms above my head crossed may have contributed ..who knows.
Not being active is definitely not on.... but finding the balance between too much or too little activity is proving a challenge for me.