It was once said to me that the way you tell whether an experience is truly spiritual or not is by its effects.
A truly spiritual experience will have entirely good effects, there will be no bad effects at all.
Whereas an experience which comes from another source may have bad effects.
Once we have had a real spiritual experience - i.e. contact with the real God - we begin to know His Name - i.e. His true nature.
And His true nature is entirely good, entirely benevolent, and entirely loving.
There is no punishment, no judgement, no violence in God.
To realize this is to know His Name.
And once we know His Name we can differentiate between what comes from God and what does not.
Photo Credit: pr1001 Flickr via Compfight cc
(The image has been slightly modified.)