After unilateral eyelid surgery, opposite eye feels like it's drooping. (Photo)

So as some surgeons have explained in response to your post, your right eyelid hasn't become more droopy. This is a case of a slight over-correction on your operated left eyelid. This is a common possible risk associated with ptosis surgery, and its not unusual for ptosis surgery to require revision (about 20% of the time).Your surgeon would definitely want to see you back soon to recommend surgeon techniques (massage/eyelid stretch) in hopes of lowering the left eyelid by 0.5 to 1 mm. If the more conservative approach is ineffective, a minor revision surgery may be required.Follow up with your surgeon soonBest regards

Thank you for sharing your question. It is not unusual for the non-operated eye to develop ptosis after the first eye is operated on. In your cases the surgical eye looks slightly higher than appropriate. It may improve, but make a consultation with your surgeon for post-op evaluation. Good luck.  

You need to see your surgeon immediately.  This is best addressed early.  Massage can be used to effectively stretch the upper eyelid.  There are very few situations where this won't correct the position of the left upper eyelid.  I suspect that if this is successfully done, the two lids will look about right.  Do not accept being told that time will resolve this issue.  It will not correct with time.  It needs active management.