When Diagnoses Overlap: PTSD, Bipolar Disorder, and Borderline Personality Disorder

If you’ve ever read about mental health diagnoses and thought,

“Wait… this sounds like me, but so does that one?”
You’re not alone. And honestly, you’re not wrong for being confused.

Today we’re talking about PTSD, Bipolar Disorder, and Borderline Personality Disorder (BPD). These diagnoses live in different sections of the DSM-5, yet often get tangled together in real life.

Many symptoms overlap, including:

• Mood instability

• Impulsivity

• Difficulty maintaining relationships

• Identity disturbance

So let’s slow this down and talk about why this overlap happens and how clinicians try, imperfectly, to tell them apart.

@the.holistic.psychologist

A Quick Reality Check About the DSM-5

The DSM-5 is phenomenological, meaning it describes what symptoms look like, not why they exist.

It organizes:

• Behaviors

• Feelings

• Thoughts

And it focuses heavily on functioning, asking how much these symptoms impair daily life.

What it does not do particularly well:

• Account for context

• Explain cause

• Fully integrate culture, race, gender, class, or oppression

• Address trauma as a root system rather than a side note

So when we ask:

• What do these symptoms really mean?

• Who decided which symptoms go where?

• Why do some diagnoses feel interchangeable?

The answer is often that human suffering does not fit neatly into diagnostic boxes.

PTSD: When the Nervous System Is Stuck in Survival Mode

What PTSD Is and Isn’t

To be diagnosed with PTSD, a person must have experienced actual or threatened death, serious injury, or sexual violence, followed by long-term symptoms in four categories.

PTSD affects about 3.6 percent of U.S. adults, roughly 9 million people. Women are diagnosed more often than men. Importantly, PTSD did not appear in the DSM until 1980, despite trauma being a human experience for as long as humans have existed.

PTSD often co-occurs with:

• Depression

• Anxiety

• Substance use disorders

Core PTSD Symptom Clusters

Re-experiencing
Flashbacks, intrusive memories, and nightmares

Avoidance
Avoiding people, places, conversations, or sensations linked to trauma
Avoiding emotions that might feel overwhelming

Cognition and Mood
Persistent shame, guilt, or blame
Feeling numb or disconnected
Memory gaps related to the trauma
Dissociation, such as feeling unreal or outside your body

Arousal
Hypervigilance
Strong startle response
Sleep disturbances
Irritability or anger outbursts

@drtraceymarks

Borderline Personality Disorder: Emotion Without an Off Switch

What “Personality Disorder” Really Means

Personality disorders are defined as enduring patterns of inner experience and behavior that develop over time, show up across many contexts, and interfere with functioning.

The DSM-5 definition of BPD emphasizes instability in:

• Relationships

• Self-image

• Emotions

• Impulse control

A person must meet five of nine criteria, which already creates a lot of variability. I encounter many people that believe they have this diagnosis due to difficulty with relationships, but that alone would not make someone fit criteria. 

In plain language, BPD is rooted in chronic difficulty regulating emotion.

Emotions tend to:

• Hit harder

• Last longer

• Take more time to settle

BPD affects about 1.4 percent of U.S. adults. Nearly 75 percent of diagnosed individuals are women, though research suggests men are likely underdiagnosed or misdiagnosed with PTSD or depression instead.

@withlovesabrinaflores

BPD Symptom Domains

Relationships
Intense fear of abandonment
Rapid shifts between idealizing and devaluing others, often called splitting

Self-Image
Unstable sense of self
Chronic emptiness or boredom

Affect
Intense depression, anxiety, or irritability
Explosive anger followed by shame
Stress-related paranoia or dissociation

Impulsivity
Risky behaviors such as spending, sex, or substance use
Self-harm or suicidal behaviors

Bipolar Disorder: Episodic Shifts in Mood and Energy

Bipolar disorder involves dramatic shifts in mood, energy, and cognition.

• Bipolar I includes full manic episodes

• Bipolar II includes hypomanic episodes and depression

While “bipolar” implies two poles, many people experience symptoms along a spectrum rather than clean extremes.

Bipolar disorder affects about 2.8 percent of the U.S. population, and nearly 83 percent of cases are considered severe.

Untreated, bipolar disorder tends to worsen. With the right combination of therapy, medication, routine, and support, many people live full, meaningful lives.

Bipolar Mood States

Mania
Severe impairment that may include psychosis or hospitalization
Seen in Bipolar I (these symptoms should persist for about a week to be considered Bipolar I)

Hypomania
Increased energy and productivity without psychosis or hospitalization
Seen in Bipolar I or II

Depression
At least five symptoms lasting two weeks, including:

• Low mood

• Loss of interest

• Sleep or appetite changes

• Fatigue

• Poor concentration

• Thoughts of death

DIGFAST: Symptoms of Mania

• Distractibility

• Insomnia, meaning decreased need for sleep

• Grandiosity

• Flight of ideas

• Activity increase

• Speech, pressured or rapid

• Thoughtless or risky behavior

@micahkohn

Why These Diagnoses Are So Often Confused

Here’s where things get tricky.

Differential Diagnosis: Real-Life Examples

Example 1: Mood Swings

• BPD: Mood shifts happen within minutes or hours and are usually triggered by interpersonal stress.

• Bipolar Disorder: Mood episodes last days to weeks and are not always tied to specific events.

• PTSD: Mood shifts often occur in response to trauma reminders or perceived threats.

Example 2: Impulsivity

• BPD: Impulsivity often emerges during emotional distress or fear of abandonment.

• Bipolar Disorder: Impulsivity appears during manic or hypomanic episodes.

• PTSD: Risky behavior may be linked to numbing, avoidance, or survival-based coping.

Example 3: Anger

• BPD: Intense anger tied to relational wounds and followed by shame.

• Bipolar Disorder: Irritability tied to mood episodes, especially mania.

• PTSD: Anger as part of hyperarousal and threat detection.

Example 4: Dissociation

• BPD: Dissociation is often stress-related and tied to attachment wounds.

• Bipolar Disorder: Dissociation is less common and may indicate severe mood episodes or psychosis.

• PTSD: Dissociation is directly connected to trauma and nervous system overwhelm.

Example 5: Identity Disturbance

• BPD: Chronic instability in self-concept.

• Bipolar Disorder: Shifts in self-perception tied to mood state rather than persistent identity confusion.

• PTSD: Identity disruption linked to trauma and survival roles.

  

The Takeaway

Symptoms do not exist in a vacuum.

They are shaped by:

• Trauma history

• Nervous system responses

• Attachment patterns

• Culture, race, gender, and class

• Access to safety and support

The DSM tells us what is happening, but it rarely explains why.

If you have ever felt mislabeled, misunderstood, or shuffled between diagnoses, that does not mean something is wrong with you. It often means the system is struggling to hold the full complexity of your experience.

You are not a diagnosis.
You are a person with a story.

And your story deserves to be understood, not just categorized.