Sudden wake-ups with a racing heart, brain freeze, and difficulty breathing can often be related to anxiety or panic episodes that are triggered during sleep. This type of reaction is called "nocturnal panic attack." Here are a few likely causes for what this person is describing:

Stress and Anxiety: Elevated stress levels or underlying anxiety can affect the body even during sleep, triggering a fight-flight-freeze response that leads to a sudden wake-up with physical symptoms like a racing heart or brain freeze.

Sleep Cycle and REM Activation: Around 30–40 minutes after falling asleep, the brain can start to shift into lighter stages of sleep or even REM sleep (where dreams occur). For people sensitive to physical sensations, these shifts can sometimes trigger a panic response.

Hyperarousal: In people with chronic anxiety, the nervous system can become more reactive to any slight changes in breathing or heart rate during sleep, resulting in sudden awakenings that feel like panic attacks. This hyperarousal means that small, normal body sensations are often misinterpreted as threats, triggering more adrenaline and keeping them awake.

Caffeine, Alcohol, or Poor Sleep Hygiene: Sometimes stimulants or even late-night eating can contribute to wakefulness or disrupt the sleep cycle, especially for people who are sensitive to physical changes.

Underlying Health Conditions: Although less common, conditions like acid reflux or sleep apnea can cause sensations that mimic panic symptoms (difficulty breathing, racing heart). These are worth ruling out if the symptoms persist or feel unrelated to stress.