| Fatigue | Feeling of tiredness or weariness usually associated with performance decrements |
| Fiberoptic Nasopharyngoscope | Flexible fiberoptic scope used in the examination of nasal passages pharynx hypopharynx and larynx. |
| Fibromyalgia | A disease syndrome whose primary symptoms are muscle pain and fatigue. |
| Flattening Index | Number indicating the amount of airflow limitation caused by partial closure of the upper airway. 0.3 indicates an open airway 0.15 is mildly obstructed 0.1 is severely limited airflow and 0.0 reflects a totally closed airway. Flattening Index is used to identify the condition known as Upper Airway Resistance Syndrome (UARS) and is continuously recorded in both diagnostic sleep studies and CPAP titrations. |
| FLIXONASE | see Beconase |
| Flow Limitation | The partial closure of the upper airway impeding the flow of air into the lungs. |
| Forbidden Zone | The period of strongest clock-dependent alerting usually in the evening. Prevents falling asleep. |
| Fragmentation (pertaining to Sleep Architecture) | Interruption of a sleep stage as a result of the appearance of a lighter stage or to the occurrence of wakefulness which leads to disrupted non-REM-REM sleep cycles. |
