I am hesitant to trust personal experiences, either of myself or by others, as a good method for determining metaphysical truth. Partially because of the above-mentioned conflicting/contradictory problem, but because of others.
First, I can attest that the only experience I've had that can be considered spiritual was the one time I used marijuana (and a lot of it). I experienced what I believed to be oneness at the time. It made me a more spiritual person for a while. But after months, I went back to where I was before. One thing that sticks out to me about the experience is how strongly a simple chemical can affect my brain. Something so mundane can cause me to perceive something that appears to me to be spiritual. That gives me serious doubts about the spiritual truth of others experiences- not that I doubt they had their experiences and that they believe them to be true, but that their experiences were indeed reflections of something supernatural instead of mere effects of our powerful and highly influential physical mind.
Secondly, I've learned of studies where other mundane things can cause certain seemingly metaphysical perceptions. Buddhist monks and Catholic nuns were studied, and were shown to be able to generate the same effect. During normal state and during intense meditation or prayer, their brains were scanned, and were shown to go through physical electrical changes. Certain parts of the brain change- especially parts that concern spatial and temporal awareness (so people feel a sense of oneness, lack of separateness, and sometimes a lack of time flow). Even more interestingly, the study showed that this effect can be re-created by sending signals of certain frequencies into the brain, and the nuns and monks verified that the induced experiences were indeed subjectively like the ones they can generate themselves.
Third, I remember watching a clip from mentalist Darren Brown where he was able to generate false subjective spiritual experiences in a group of atheists and agnostics. He's a hypnotist that does tons of amazing stuff, and in this scenario he interviewed some people about their beliefs or lackthereof, and was able to convince several of them to believe in something supernatural with hypnosis. He just talked to them in a big room, and was able to do things like make people fall over and feel a presence and higher truth, and then at the end deconverted all of them by telling them he doesn't necessarily believe in that stuff and that it was all an exercise. He of course didn't want to permanently alter someone's lifeview based on a trick.
How is this addressed by those with experiences?