Strange feeling in eye after under eye fillers. Is this a normal side effect?

There is a large sensory nerve called the infraorbital nerve that emerges through the bone just under the eye socket; this nerve supplies sensation to the cheek and lower eyelid.  Irritation to this nerve, such as from injections in the tear troughs, may lead to some of the heavy and/ or numb sensations you describe.  The chance of this leading to vision loss, especially 1 week out from filler placement, is very, very low: I wouldn't worry about this.  It is normal to feel the filler product underneath the skin, especially the thin skin of the lower eyelid, for the first few weeks after injection; the filler can take a few weeks to settle into the tissues.  Please check in with your treating physician to discuss your concerns and undergo an exam.  Good luck!