Sforno on Genesis 20:3/ספורנו על בראשית כ׳:ג׳

1ויבא אלוקים אל אבימלך, this visitation was of a similar kind to that reported with Lavan (31,24) and Bileam (Numbers 22,24) respectively. The Torah refrains from speaking about a מחזה, “a vision,” in order not to place these wicked people on a pedestal similar to our patriarchs. The expression דבור to describe a verbal communication to these individuals is also absent, G’d having reserved such an expression for communications with prophets, as He pointed out to Miriam and Aaron in Numbers 12,6. Avimelech did not experience a visual image of G’d in his dream at all. He perceived a divine voice addressing him.

2הנך מת, the impotence which you experienced (verse 18) will result in your death.