After treatment, Kaikai returned home from the hospital completely exhausted. She slept through the night, yet woke up feeling just as drained as before. With ordinary tiredness, rest usually brings relief. This exhaustion, however, did not improve. That was when Kaikai learned about cancer-related fatigue (CRF).

Normal fatigue is the body’s natural signal that rest and recovery are needed. It typically follows physical or mental effort and improves with sleep. Cancer-related fatigue is fundamentally different. It is deep, persistent, often disproportionate to activity, and does not fully resolve with rest or sleep. CRF develops because cancer and its treatments affect multiple body systems at the same time, rather than having a single cause.

Why Cancer-Related Fatigue Feels So Overwhelming

Cancer-related fatigue feels overwhelming because cancer and its treatments affect multiple body systems at the same time. Rather than a single cause, CRF develops from the combined strain placed on the entire body.

Key Body Systems Involved

• Cellular energy systems
• Immune system
• Blood and oxygen transport system
• Nervous system
• Hormonal (endocrine) system
• Lymphatic system
• Sleep and circadian rhythm system

When several of these systems are stressed simultaneously, the body struggles to restore energy, resulting in deep, persistent fatigue.

Cancer treatments place stress on cells to help destroy cancer. At the same time, this stress can also affect healthy cells—especially the parts responsible for producing energy. When the body’s energy supply is disrupted, muscles feel weak, focus declines, and stamina drops. The result is a deep, whole-body exhaustion that sleep alone cannot relieve.

At the same time, the immune system remains on high alert to protect the body. While this response is necessary, it uses a significant amount of energy. As energy is redirected toward healing and defense, less is available for everyday activities. This can lead to physical discomfort, heaviness, and ongoing fatigue that does not easily improve with rest.

Cancer treatment can also affect the blood’s ability to carry oxygen. When oxygen delivery is reduced, the body must work harder to create energy. As a result, people may experience weakness, shortness of breath, or mental fog. Even small reductions in oxygen supply can significantly worsen fatigue.

The nervous system is often affected as well. Cancer can activate the sympathetic nervous system (the fight-or-flight response) while reducing the activity of the parasympathetic nervous system (the rest-and-repair system). This imbalance can lower levels of key neurotransmitters such as dopamine, serotonin, and GABA, which support motivation, mood, calmness, and sleep. When these systems are out of balance, fatigue is felt not only physically, but mentally and emotionally as well.

Hormonal regulation may also be disrupted. Cancer and its treatments can affect the endocrine system (the body’s hormone-regulating system), leading to lower thyroid hormones, which slow metabolism and reduce energy. Changes in cortisol (the stress hormone) , creating a “tired but wired” feeling. Levels of sex hormones such as estrogen or testosterone may also decrease, affecting motivation and overall vitality. Together, these hormonal shifts can intensify fatigue and interfere with restful sleep.

The lymphatic system, which helps remove waste, toxins, and excess fluid, may also slow due to surgery, radiation, inflammation, or reduced movement. When lymphatic flow is impaired, people may experience swelling, heaviness, pressure sensations, and increased fatigue. Slower waste clearance can leave the body feeling burdened and depleted.

Sleep disruption further compounds fatigue. Sleep is essential for tissue repair, restoration of energy systems, and clearing waste products from the brain. During cancer and its treatment, sleep may be disturbed by pain, anxiety, steroid medications, night sweats, altered stress hormone rhythms, and hospital routines. Without deep, restorative sleep, the body cannot fully recover, allowing fatigue to accumulate over time.

Taken together, cancer-related fatigue is not simply “being tired.” It reflects widespread strain across the body—impaired energy production, chronic inflammation, reduced oxygen delivery, nervous system imbalance, hormonal disruption, slowed lymphatic flow, and incomplete recovery during sleep.

When Movement Becomes Medicine

So what can help?

For Kaikai, understanding what was happening inside her body was the first step. Knowing that her exhaustion had real biological roots—not weakness or lack of effort—brought relief. She also learned that gentle movement, when done mindfully and appropriately, could support recovery rather than drain her further.

Research shows that gentle movement—especially yoga and other mindful practices—can support multiple body systems at the same time, making it particularly effective for managing cancer-related fatigue and treatment side effects. Gentle movement improves blood flow and oxygen delivery, helping the body create and use energy more efficiently. Yoga has also been shown to calm inflammation by reducing inflammatory signals such as IL-6, TNF-α, and NF-κB, supporting immune balance and easing fatigue (Sharma et al., 2014; Bower et al., 2019).

Movement-based practices also help activate the parasympathetic nervous system (the body’s rest-and-recovery system), allowing the body to shift out of constant stress mode. Practices such as slow, gentle yoga postures, mindful breathing, and Yoga Nidra calm brain activity and encourage deep physiological rest. Improved sleep quality appears to be a key mechanism by which yoga reduces fatigue. Large clinical studies show that better sleep explains a significant portion of yoga’s fatigue-reducing effects (Mustian et al., 2018).

Strong clinical evidence supports these benefits. In a Phase III randomized controlled trial involving over 400 cancer survivors, a four-week yoga program significantly reduced cancer-related fatigue compared to standard care (Mustian et al., 2018). Other studies show that yoga can reduce inflammatory gene expression, stabilize inflammation-related markers, lower oxidative stress during treatment, and improve overall quality of life (Sharma et al., 2014; Sethi et al., 2023). Meta-analyses consistently find that yoga and mindfulness-based practices have meaningful positive effects on cancer-related fatigue (Kirkwood et al., 2022).

A Compassionate Path Forward

In summary, cancer-related fatigue is a real, complex, whole-body condition arising from the combined effects of cancer and its treatment. While it can feel persistent and overwhelming, evidence shows that gentle movement, along with adequate rest, nutrition, and appropriate medical care, can significantly reduce fatigue and improve quality of life.

For Kaikai, this understanding marked a turning point. Rather than pushing herself to “get back to normal,” she began listening to her body and supporting it with mindful movement, breath, and rest. With yoga as a companion in her recovery, she started rebuilding energy—not by forcing it, but by allowing her body the time and support it needed to heal.