Internal tremors are a subjective feeling of vibration, buzzing, or shaking deep inside the body, often described as being felt but not seen. Unlike external tremors, which involve visible, rhythmic movement, internal tremors are thought to arise from the same neurological mechanisms as visible tremors. This hidden shaking can occur in the arms, legs, chest, or abdomen. The perception of this movement is often amplified when the body is at rest.
Why This Sensation Occurs When Lying Down
The feeling of internal shaking is frequently most noticeable when a person is lying down or sitting still, a phenomenon rooted in sensory amplification. When the body is highly active, the brain is flooded with external sensory information and signals from muscle movement, which effectively masks subtle internal sensations. When lying down, external stimuli and muscle activity are dramatically reduced, creating a quiet sensory environment. This stillness allows the brain to perceive subtle physiological signals that were previously ignored. Natural, rhythmic movements, such as the pulse or minute muscle twitches, become more prominent, and reduced muscular tension allows low-amplitude neurological signals to be sensed more clearly.
Common and Benign Triggers
In many instances, the perception of internal shaking is linked to temporary physical states or lifestyle factors that heighten nervous system sensitivity. High levels of stress and anxiety are a frequent cause, triggering the body’s “fight or flight” response. This response releases stress hormones like adrenaline, which overstimulate the nervous system. This overstimulation can cause an internal feeling of jitteriness or trembling, even without visible external movement.
Consumption of stimulants, most notably excessive caffeine, can also induce this feeling by increasing central nervous system activity. Similarly, the body may experience a temporary state of hyperexcitability during withdrawal from substances like alcohol or certain medications. This rebound effect causes a surge in nervous system activity that translates into the sensation of internal vibration.
Another common trigger is muscle fasciculation, or small, involuntary muscle twitches. These twitches are often harmless but can be amplified by fatigue, strain, or a lack of sleep, which compromises muscle control. Certain common medications, including some antidepressants, asthma drugs, and corticosteroids, can also have a stimulating effect on the nervous system, leading to enhanced physiological tremor that is felt internally.
Underlying Conditions Requiring Investigation
Metabolic Causes
While many internal tremors are benign, the symptom can also be an early manifestation of a systemic medical issue requiring diagnosis and treatment. Metabolic disorders significantly impact nervous system function. For example, hyperthyroidism (an overactive thyroid) floods the body with excess thyroid hormones, which act like stimulants and cause generalized overstimulation of the nervous system and muscles.
Fluctuations in blood sugar, such as hypoglycemia (low blood sugar), can also provoke internal tremors. When glucose levels drop too low, the body releases adrenaline to trigger the release of stored glucose, resulting in a physical feeling of shakiness. Deficiencies in certain micronutrients, such as Vitamin B12 or magnesium, can also disrupt nerve signal transmission and muscle function, potentially contributing to the internal sensation of vibration.
Neurological Conditions
Internal tremors are also recognized as a potential symptom of certain neurological conditions. Essential Tremor (ET), a movement disorder that typically causes a visible action tremor, is frequently reported to include an internal tremor component. Early-stage Parkinson’s disease, while classically associated with a visible resting tremor, may also begin with a subjective feeling of internal vibration, often accompanied by other symptoms like stiffness or slow movement.
When to Seek Medical Guidance
If internal tremors are persistent, worsening, or interfere with daily tasks, a medical evaluation is warranted. It is important to seek professional guidance if the tremors are accompanied by other physical changes, such as unexplained weight loss, a rapid or irregular heart rate, muscle weakness, or difficulty walking. These symptoms can indicate underlying metabolic or neurological issues. To prepare for a doctor’s visit, keep a detailed log of the symptoms, noting triggers, duration, and occurrence. Diagnosis typically involves a medical history, physical exam, and blood tests to check for thyroid function, vitamin levels, and other metabolic markers.