| IH | Idiopathic Hypersomnia |
| Imidazopyridines | New class of compounds inducing sleepiness. (Zolpidem trade name Ambien is in this class). |
| Inappropriate Sleep Episodes | Unplanned sleep periods often occuring in an unsafe situation (i.e. while driving). These episodes are always due to sleep deprivation. |
| Insomnia | Complaint describing difficulty in sleeping |
| INSOMNIA (in-som-nee-ah) | Being awake when you want to be asleep. Often thought of as a problem but may not be. Common if people try to spend too long in bed. |
| Inspiratory Phase | Part of the breathing cycle in which air is inhaled. |
| Inspiratory Positive Airway Pressure (IPAP) | Physician prescribed pressure for the inspiratory phase on a Bi-level CPAP device used in the treatment of OSA. |
| Invasive | Referring to a medical procedure in which a bodily orifice or the skin must be penetrated for the purpose of collecting data or for diagnosing or treating a disorder |
| IPAP | Inspiratory Positive Airway Pressure |
| IRM | Institute of Respiratory Medicine |
| ITS | I'm Tired Syndrome |
