Random overnight lip swelling after Juvederm -- is this an allergic reaction? (Photos)

This isn't typical. I recommend following up with your injector. If necessary, the juvederm can be reversed with hyaluronidase. I hope this helps

Delayed swelling is a phenomenon with any HA filler. Typically there is no apparent reason for the sudden swelling. I would see your injector and discuss hyaluronidase. In some cases a brief course of steroid can help. Good luck. 

It's difficult to know what your lips are reacting to.  I would recommend going back to your provider and having her put more hylenex into your lips in order to dissolve the remaining filler, just in case you are reacting to that.  I would also recommend that you pay close attention to what you eat/drink right before this happens.  You might be allergic to something that is coming into contact with your mouth.

The description of your symptoms may suggest a delayed allergic reaction to the filler. This type of reaction is unpredictable. I am not sure whether your photos are in between the episodes or at the time  of swelling. It seems that at the time of your photograph your upper lips is disproportionally fuller and there is overall asymmetry. The only thing to address it is another hyaluronidase injection in attempt to dissolve it all and possible oral steroids. Your injector will most likely find the solution and determine whether there is also a possibility of granuloma formation. Good luck!