Do not give in to your inclination to think about ghosts and apparitions; rather keep your mind solely on God's Name and meditate on Him. In the presence of His Name no other power can function. This is the truth, be firmly convinced of it.
The moment you have recourse to God's name you should feel that no lesser power can touch you. If at that time you are aware of any physical anxiety, be quite certain that it is merely a bodily reaction.
Please check these: Excerpts from a discourse by our Sri Sri Muralidhara Swamiji
He was walking in the jungle, he heard a distant roar of a wild animal. He immediately cried out 'Krishna! Oh Krishna! My brother where are you?' Since he called out, our Lord Krishna's Name with so much faith and devotion, Lord Sri Krishna appeared before him in all His beauty.
Just as the dawn dispels the darkness and rids one of fear from thieves and ghosts, the chanting of the Divine Names also rids one of all sins and bestows liberation as soon as it is chanted. But that is not the intention of chanting the Divine names.