One test of a grace is: how do we use it ? If someone is improved by what they think is an extraordinary grace, that is a good sign: it could, perhaps, be God-given.
If OTOH someone supposes themselves to have received some kind of favour from God, & is none the better for it - then they can forget about it: it’s their psyche or their hormones or some other merely human thing; not God. If someone claims to have had a vision, but continues in grave sin, they are extremely likely to be deceiving themselves.
We must avoid being fanciful, & elevating every unusual feeling we have into Divine action: the danger in being fanciful is that if & when we ever receive the Real Thing in this world, we will dismiss it as a fancy, as a result of having found that previous fancies were no more than fancies . Our sanctification does not lie in having spectacular experiences, but in being obedient to the Will of God so far as we know it: St. Bernardette is a Saint because of her God-given holiness - not because of her visions. Having “religious experiences” is proof of nothing - what matters is how one responds to them. We are not damned if we see no miracles or visions - we are damned if we die without love of God: for that, is worth all the visions & what-not in creation.