I've never actually guided somebody through a DMT trip, so I can only speak from my own experience. And everybody's experience is likely to be different.
My experience with psychedelics in general is that some amount of panic is likely to pop up at some point. The key for me when I get those feelings is just to let go and submit to the substance COMPLETELY. Once reality (as you know it) starts to crumble, the ego has a tendency to tell you, "This isn't right. Everything is fucked up. I'm not supposed to feel like this. Holy shit, I'm dying!" This is where the term "ego death" is often brought up. You have to be able to say "Fuck you ego. We're doing this shit and it's gonna be fucking awesome." Then take a deep breath, relax and buckle up for an amazing ride.
I've had a couple trips that started off with some anxiety, but by the time the I fully blasted off it put me in such a beautiful and blissful place where anxiety just didn't exist anymore. At that point I'm just in awe at what I'm seeing and feeling. And I really believe once you get "there" for the first time and "come back" safe and sound, you'll be more likely to wanna go back again and those worries will be a thing of the past.
Things to remember going into the experience... DMT will not kill you. And the trip is so short, you will be back to "normal" in almost no time. And you have to remember that you're taking a substance that is intended to distort reality and there will be absolutely nothing "normal" about it. Don't try to fight it or control it. Let it have its way with you. It will love you unconditionally in ways you never imagined. Even if it does take you down a temporary dark spiral, you can't be fearful or try to fight in that moment. It might be trying to show you something you've been struggling with subconsciously and bring it to the surface. It might also give you the answers you're looking for to get through that pain and show you that everything will be ok. It always seems to remind me that the things I stress about are so tiny in comparison to the bigger picture and they're not even worth the energy I give them.
Now I really can't speak on using DMT on anti-depressants. I've tripped on alprazolam and had some amazing experiences even though many people claim it would kill the trip. I also understand that SSRI's and SNRI's affect the brain differently than benzos. I have heard that MAOI's and SSRI's can be a potentially deadly combination. But as long as you're smoking DMT with no MAOI, I imagine it's safe. Though some say the experience may be lessened due to the anti-depressants. So it's possible you're dealing with that. It does sound like you were very close to a breakthrough though. One more hit may have sent you there.
I'd highly recommend sitting somewhere and remaining seated through your experience though. Pacing around the garage high on DMT is much more dangerous than just using DMT by itself. It's best to lay back in bed or on the couch while you're blasting through hyperspace. A relaxing/safe set and setting may also help you put your mind at ease and open yourself up to take on the adventure.
I wish I could be of more help. Again, I can only speak from my own experiences. But I wish you the best of luck on your DMT journeys going forward.
Death & Reincarnation Under God's Supervision​