Wake and Sleep State Transitions on a Portable Electroencephalogram (EEG) Device in Narcolepsy Type 1 (NT1) and Healthy Participants

Inclusion Criteria: 1. Has access to at-home Wi-Fi and can add an internet-ready device with assistance. 2. Body mass index (BMI) between greater than equal to (\>=) 18.0 and less than or equal to (\<=) 40.0 kilogram per square meter (kg/m\^2) at the screening visit. 3. Must have regular sleep-wake habits (example, routinely spending 6.5 to 8.5 hours sleeping nightly, not oversleeping by more than 2 hours on weekends, that is, total sleep not more than approximately 10.5 hours) as determined by investigator interviews and confirmed in accelerometry/actigraphy records obtained between screening and first visit (measured using a minimum of 10 day/night consecutive periods) and who regularly fall asleep between 9:30 PM and 12:00 AM (healthy participants only). 4. Must not require use of sleep aids or must be willing to discontinue use of sleep aids for the duration of the study. 5. Has completed the TAK-994-1501 study, the participant is eligible to enter the current study following the appropriate washout period (60 days). Participants With NT1 Only: 1. With NT1 who is drug-naïve may also be enrolled. 2. With NT1 must present with subjective sleep complaint. 3. With NT1 must have a diagnosis of NT1, as defined by the International Classification of Sleep Disorders, 3rd edition (ICSD-3) criteria. Exclusion Criteria: 1. Has a current diagnosis of cancer except for squamous or basal cell skin cancer. 2. Has a nicotine or marijuana dependence that is likely to have an effect on sleep (example, a participant who routinely awakens at night to smoke) and/or an unwillingness to discontinue all smoking and nicotine use during the confinement portions of the study. 3. Cannot maintain stable sleep environment at home, for example, due to young children not yet sleeping through the night or partners with disrupted sleep (example, shift workers). 4. Undergoing current treatment for hepatitis B with interferon. 5. Has a risk of suicide according to endorsement of Item 4 or 5 of the screening visit Columbia Suicide Severity Rating Scale (C-SSRS) or has made a suicide attempt in the previous 6 months. 6. Has medical condition, such as past or current epilepsy, seizure, head injury/trauma, medically significant unstable cardiovascular, pulmonary, hepatic, renal, or gastrointestinal disease, that interferes with a normal sleep pattern or would preclude enrollment in the view of the investigator. 7. Has a lifetime history of major psychiatric disorder, such as bipolar disorder or schizophrenia. 8. As of the screening visit and throughout the study, the participant should not be a chronic caffeine user, as defined by an excessive (greater than \[\>\] 600 milligram \[mg\]/day) caffeine intake per day. 9. Has a medical disorder (other than narcolepsy), associated with excessive daytime sleepiness. This includes clinically significant obstructive sleep apnea or other sleep disturbances that has a significant impact on daytime sleepiness, confirmed by past PSG data (example, apnea hypopnea index \>=10, periodic limb movement disorder index in sleep \>=15) or a periodic limb movement disorder arousal index of \>=10, or as evaluated on interview at the screening visit. Because nPSG data is obtained on Day 1, participants may be removed from study if they meet the above exclusion at the discretion of the principal investigator. Participants removed under this criterion will be replaced. 10. At the time of screening the participant is being treated with nasal or oro-nasal positive airway pressure for any reason. 11. Is currently being prescribed sodium oxybate or has been off of sodium oxybate for less than 4 weeks. 12. Is using varenicline (Chantix).