How is ADHD linked to intermittent fatigue and highs? 

Many adults with ADHD notice a pattern of feeling unexpectedly exhausted at some points in the day and unusually energised at others. According to NHS information, this fluctuation is linked to how ADHD affects concentration, emotional regulation, and the brain’s reward system, all of which influence day-to-day energy levels (NHS). NICE guidance also explains that because people with ADHD work harder to maintain focus and organisation, their mental energy can drop more quickly than expected (NICE NG87). These changes can feel confusing, but they reflect real neurological factors rather than a lack of effort or motivation. 

Understanding fluctuating energy in adults with ADHD 

Adults often describe fatigue appearing suddenly after periods of focus or emotional intensity. This pattern is closely tied to the additional cognitive load the ADHD brain manages throughout the day. NHS guidance highlights that disrupted or delayed sleep is common in ADHD and directly contributes to daytime tiredness, especially when combined with stress or overstimulation (NHS). 

Why fatigue happens in ADHD 

Research shows that dopamine and noradrenaline regulation in ADHD affects the brain’s ability to sustain motivation and alertness, which can make even routine tasks mentally exhausting. A review notes that this lower baseline activation forces the brain to work harder, leading to quicker burnout (PubMed). Emotional demands also play a part. The Royal College of Psychiatrists explains that difficulties with emotional regulation can create cycles of stress, overwhelm, and exhaustion that feel sudden and hard to predict. 

Why “highs” or bursts of energy occur 

Short bursts of energy often appear when a task is interesting, urgent, or rewarding. The Royal College of Psychiatrists describes this as hyperfocus, where attention becomes temporarily enhanced in response to stimulation (RCPsych). Reviews also show that dopamine can surge when the brain encounters novelty, producing brief periods of heightened motivation (PMC). NHS Dorset notes that stress or approaching deadlines may trigger “crisis mode”, where adrenaline boosts energy even if fatigue was present earlier. 

Key takeaway 

Fluctuating energy is a recognised part of ADHD. Evidence from the NHS, NICE, and clinical research shows that sleep challenges, emotional load, dopamine differences, and executive effort all contribute to sudden fatigue and short-lived highs. Understanding these patterns can make the experience feel less confusing and more manageable. 

Harriet Winslow, BSc

Author

Harriet Winslow is a clinical psychologist with a Bachelor’s in Clinical Psychology and extensive experience in behaviour therapy and developmental disorders. She has worked with children and adolescents with ADHD, autism spectrum disorder (ASD), learning disabilities, and behavioural challenges, providing individual and group therapy using evidence-based approaches such as CBT and DBT. Dr. Winslow has developed and implemented personalised treatment plans, conducted formal and informal assessments, and delivered crisis intervention for clients in need of urgent mental health care. Her expertise spans assessment, treatment planning, and behavioural intervention for both neurodevelopmental and mental health conditions.

All qualifications and professional experience stated above are authentic and verified by our editorial team. However, pseudonym and image likeness are used to protect the author's privacy.

Dr. Rebecca Fernandez, MBBS

Reviewer

Dr. Rebecca Fernandez is a UK-trained physician with an MBBS and experience in general surgery, cardiology, internal medicine, gynecology, intensive care, and emergency medicine. She has managed critically ill patients, stabilised acute trauma cases, and provided comprehensive inpatient and outpatient care. In psychiatry, Dr. Fernandez has worked with psychotic, mood, anxiety, and substance use disorders, applying evidence-based approaches such as CBT, ACT, and mindfulness-based therapies. Her skills span patient assessment, treatment planning, and the integration of digital health solutions to support mental well-being.

All qualifications and professional experience stated above are authentic and verified by our editorial team. However, pseudonym and image likeness are used to protect the reviewer's privacy.