I never thought much of odd occurrences—those small, weird moments that, at first, seem insignificant. If anything, I was the kind of person who shrugged them off. So, when I found a yellow Post-it note on my desk one morning, I didn’t think much of it at first.

The handwriting was shaky and unfamiliar, reminding me to pick up cucumbers and crackers for groceries and to mail a letter. Things I had considered doing, but never told anyone about. Yet there it was, sitting on my desk like an eerie to-do list.

I scanned my phone to see if I’d set a reminder and forgotten about it, but there was nothing. Maybe I wrote it down half-asleep or my brain was playing tricks on me. After all, who even mailed letters anymore? I didn’t. I emailed people, unless it was a package I needed to send. But there was no package. Still, I shrugged it off, tossing the note in the trash.

A few days passed, and then another note appeared. Same yellow Post-it, same shaky handwriting: Make sure you save your documents.

That one made me pause. It was a little stranger than the first, but still, I dismissed it. I was a freelance writer, after all. I’d been working on a big project the night before. There was no reason to panic, I told myself. I lived alone, my door was locked, and there were no signs of a break-in. Still, the oddity lingered in the back of my mind.

The next night, I woke to another note. This one was different, more disturbing. Our landlord isn’t letting me talk to you, but it’s important that we do.

That sent a chill down my spine. Who was writing these? And why was my landlord suddenly involved? I jumped up, checked the locks, checked the windows—everything was secure. My landlord had a key, but it seemed out of character for him to come in without prior arrangement. I felt unsettled. Surely, I could find proof—my webcam. I’d set up an old webcam to record movement, just in case.

I rushed to check the files. They were gone. Completely erased. Panic gripped me. How was that possible? No one else had access to my laptop, right?

But then it hit me—someone had been inside my apartment. Someone who knew about the camera, someone who had the ability to erase the footage. My stomach twisted as the realization sank in.

I couldn’t sleep. My mind raced with possibilities, and I had no answers. I grabbed a knife from the kitchen, double-checked the locks again, and stayed in bed, though I couldn’t close my eyes. Something was terribly wrong.

The next day, after my gym session, I returned to my apartment to find a blank Post-it note stuck to my door. Just a pale yellow square, no message, no handwriting—nothing. My hands shook as I tore it off. Was someone watching me? Did they know I was aware of the other notes? Did they know I wasn’t home?

A sick feeling churned in my stomach as I noticed the same kind of Post-its on other doors in my building—some yellow, some pink, some blue—but all blank. Had this been happening to everyone? Was I the only one who noticed? I couldn’t wait any longer. I needed help.

I ran to my neighbor’s apartment, desperate for reassurance. Jessica answered in a disheveled state, clearly surprised to see me.

“Mila? What’s going on?” she asked.

I pushed past her, frantic. “I need you to tell me I’m not crazy.”

She blinked, rubbing her eyes. “Okay, but we’re going to need some coffee. And I swear, if this is about aliens again, I’m going to smack you with something.”

“No,” I said, snapping. “This is worse. Someone’s been in my apartment.”

Her eyes widened as I recounted everything—the notes, the deleted footage, the locked door, the missing phone. I could barely keep it together as I spoke. Her silence as she listened made the fear inside me grow.

She finally spoke, her voice soft. “But there’s been no sign of anyone else being there?”

“Nothing! I can’t make sense of it. There’s no break-in. No footprints. But the notes, the deleted footage… it doesn’t add up.”

Jessica paused, her brows knitting together in thought. “Have you checked for carbon monoxide?” she asked, almost casually.

“Carbon monoxide?” I repeated, confused.

“CO poisoning,” she explained. “It can cause memory issues, disorientation, and paranoia. What if you’re writing the notes yourself and just not remembering it?”

I stared at her, stunned. I’d been feeling off lately—headaches, exhaustion, cloudy thoughts. Could it really be possible? Was my brain betraying me?

I didn’t waste any time. I ran to a nearby gas station and bought a carbon monoxide detector. The moment I plugged it in, the reading shot up: 100 parts per million.

The dizziness hit me before I even had a chance to process the numbers. The air felt thick and suffocating, and panic surged through me. I grabbed my bag and rushed outside, desperate for fresh air.

“Jess, I need you now!” I gasped when she picked up the phone. “The reading was insane!”

“I’m coming. Stay outside, Mila. Get some fresh air.”

At the hospital, the doctor explained what had been happening. “You’re lucky you caught this when you did,” he said, flipping through my chart. “Prolonged exposure to 100 ppm could’ve been deadly. You weren’t in immediate danger of suffocating, but without treatment, it could have caused permanent cognitive damage. You might have lost consciousness and never woken up.”

“How long would I have had?” I asked, my voice barely a whisper.

“Weeks, maybe less. Carbon monoxide poisoning is no joke,” he replied grimly.

My mind was racing as I processed the information. I thought I had been paranoid. I thought I had been losing my mind. But the truth was far scarier.

I called my landlord, Greg, to ask about the gas leak. His response was less than reassuring. “We’ll get it checked,” he muttered before quickly hanging up. I decided to take matters into my own hands and called the city inspector. That’s when I learned the true nightmare: the carbon monoxide wasn’t just in my apartment. It was coming from the building’s parking garage, and my unit was directly above it.

I had been breathing in the toxic fumes for weeks, unaware that my apartment had become a slow-motion death trap. Greg knew about the leak but hadn’t done anything. When I confronted him, he was dismissive, offering no real answers.

“You knew,” I told him. “You knew about the leak. How long has it been there? How many other tenants have complained?”

His jaw clenched. For a moment, something flickered in his eyes, but then it was gone, replaced by a cold indifference. “I don’t know what you’re talking about,” he muttered.

It was clear that I wasn’t the first person this had happened to—and I wouldn’t be the last. The truth had been right under my nose all along, hidden in plain sight, and I almost didn’t make it out in time.

I learned a crucial lesson: sometimes, paranoia isn’t paranoia at all. Sometimes, it’s survival. If something doesn’t feel right, don’t ignore it. And if you start noticing things out of the ordinary, trust your instincts—they might just save your life.