There are two questions here. One does Satan exist and if so what is he or it? And two what causes bad dreams. We’ll deal with the second question:
Where do dreams come from?
Most dreams appear to arise from within our own subconscious minds (e.g., Eccles 5:3), although the Bible describes some dreams as coming from God himself (Numbers 12:6). The following passages list all the places where God sends dreams:
|Genesis 20:3-7; 28:12-15; 31:10-13, 24; 37:5-9; 40:5-23; 41:1-8; Judges 7:13; 1 Kings 3:5-15; Daniel 2:1-45; 4:4-18; 7:1-28; Matthew 1:20-24; 2:12,13,19-20,22; 27:19.|
Nowhere in the Bible does it describe a dream coming from any source other than God or our own minds.
And what about Satan?
Well please search this site for other answers. Basically Satan is an allegorical figure that was introduced late into two poetic writings in the Old Testament and taken up as a bigger allegory by Jesus in the New Testament. Satan doesn’t exist as an actual being.