I'm probably unhealthy, but I don't abuse any substances.
However, I am very depressed. And I have a tendency to think very hypothetically, and my mine gets cluttered with analysis of all the things I could possibly do right now, with my life, and about my life, and I collapse under the weight of my doubts and assumptions, and find myself doing nothing at all, withdrawing further into my room, into my mind, and become neurotic.
So how's that?
Sounds like you should start abusing substances.
Listen to me, baby, you got to understand, you're old enough to learn the makings of a man.
I can't identify with the substance abuse too much, but I become increasingly more nihilistic when I become unhealthy. Much like I am right now.
I get to the point where I'm shut off from the world and wondering if there's even a point to seeking pleasure anymore. I get driven by fear into just sitting in my room and not showing anyone how I'm feeling.
I have a problem with sharing anything with people, when I'm unhealthy it gets really difficult because of that problem and just exacerbates things.
Can a true INTP be psychologically healthy and happy, though, really?
I can't imagine it, they are utterly neurotic, and pessimistic by nature.
The closest thing to a smile they can muster is a smirk.
EDIT: Admittedly, I was thinking about my (unwell, and dead ) INTP father as I was writing that thought.
I'm actually a happy and calm person by default. My friends always commented on my deafening laugh. I blame undeveloped Fe for not knowing how to laugh "appropriately"; I sound like a seagull fighting for a bag of chips.