We are not fully trusting in Jehovah's promises and relying totally on Him to be our defense, provider, guide and healer. We would rather trust in what we can feel, hear, touch, smell, and see. We trust our own physical senses more than we trust in the invisible Creator of the Universe. Because they knew they had now placed themselves in disobedience to God and therefore subject to His judgment. They will run and hide, just like Adam.
Disobedience brings separation.
We put our criminals behind bars to separate them from the rest of society. And God had decreed already to Adam that if He disobeyed His direct command, then separation would occur. Death would result. The commuted sentence of eternal separation where no more grace, mercy, love or kindness would begin . So Adam feared.