Just about everybody must have experienced this weird phenomenon—you feel suddenly like you're falling, and wake up with a jolt only to realize you've been lying in bed all along. This often happens just as you're falling asleep, and it's technically not a dream so much as an involuntary muscle movement know as a hypnic jerk, or a sleep start.
Despite how common this is, nobody is exactly sure why it happens. Experts suggest that it's probably the result of a conflict between the waking and sleeping systems of your brain, with both sides struggling for control as you make the transition into sleep. On some nights you slip effortlessly into slumber, but on other nights the waking brain puts up more of a fight—whether because of stress, caffeine, adrenalin, medication, hormones, etc—which is when you end up plummeting from an imaginary cliff.
2. School & exams
It seems really, really unfair that even years after graduation, the horror of the exam hall still haunts us. If you've ever dreamed that you're about to take a crucial test you forgot to study for, or that you've accidentally forgotten to go to class all year, you're not alone—school anxiety dreams are among the most common of all.
Studies have found that our strongest memories tend to be from adolescence and early adulthood, which might be why you're still dreaming of school years after you left—even if your real anxiety is about your current job, your subconscious mind interprets it through those earlier, stronger classroom memories.
Neurology news website Braindecoder found that school-based nightmares were especially common among type-A overachieving types, who have probably never missed a day of school in real life.
3. Being chased
You've seen terrifying chase sequences in a million horror movies, and chances are you've seen at least one or two behind your eyelids too. According to some researchers, this is the most common nightmare of all, and it's an expression of our innate fight-or-flight instinct.
Everyday stressors can spike adrenalin levels just like a predator would in the wild, and the subconscious impulse to run away emerges in dreams. Bustle has a pretty great breakdown of the different types of chase dream—turns out that dreaming you're being chased by a person means something very different than if you're being chased by an animal.
4. Malfunctioning technology
It may seem a little lacking in drama compared to the rest, but anyone who's ever cried in front of an faulty printer knows that this kind of anxiety dream is no joke.
Scary tech dreams come in all shapes and sizes—buttons on a remote aren't where they should be, a telephone refuses to connect, or maybe your computer just dies down without warning. These dreams can suggest anxiety about making emotional connections, or anxiety about the mechanical workings of your own body.
Unsettling though they are, dreams about death or serious illness are some of the most common of all, and they're not a harbinger of real-life doom. Dream analysts generally agree that dreaming about death indicates something in your life is coming to an end—whether that be a relationship, a job, an era, or something more abstract. Death is the great unknown, so morbid dreams can also indicate that you're feeling anxious about a situation in your life that is uncertain or ambiguous.