Timing and type of last meal prior to the first dose will be collected using both Daily Diary and Weekly Lookback of Daily Diary. The timing will be collected as actual time (HH:MM) from Daily Diary and as categorical data of usual number of hours relative to first dose (<0.5 hours, ≥0.5 but <1 hours, ≥1 but <1.5 hours, ≥1.5 but <2 hours, ≥2 hours) from Weekly Lookback of Daily Diary. In order to evaluate the timing of last meal across all study periods, the Daily Diary entry will be converted into categorical data using the same value scale as Weekly Lookback of Daily Diary. The type of last meal prior to the first dose will be collected as categorical data (regular meal, snack, and beverage). For both timing and type of last meal prior to the first dose, the number of participants with each response will be summarized.

The number of participants who discontinued Xywav administration during the Xywav Treatment Period (Period 2 to 5).

The PGI-C is a series of self-administered questions designed to measure the meaningfulness of change in symptoms following an intervention. The PGI-C is used to assess the change in excessive daytime sleepiness, cataplexy, and short- and long-term nausea since the transition from Xyrem to Xywav. It is a 7-point Likert-type rating scale from 1 = very much improved, 2 = much improved, 3 = minimally improved, 4 = no change, 5 = minimally worse, 6 = much worse, to 7 = very much worse. The score is the sum of responses to each of the answer choices.

Sleep pattern (how long usually took to fall asleep after the first dose, how long usually spent awake during the night) will be summarized. Sleep pattern and quality will be collected using both Daily Diary and Weekly Lookback of Daily Diary. The number of participants with each response to sleep quality (very poor ~ very good) and feeling on how rested/refreshed when woke-up for the day (not at all rested ~ very well rested) will be summarized by day and by week. In order to analyze the data together the intention is to combine the daily by deriving the categorical frequency for the responses so that it can be combined with the categorical data collected in the weekly diary. Which will allow for a full analysis of the change from the Baseline period (Xyrem) to Xywav Treatment Period (Period 2 to 5) will be summarized for weekly data collected during the Xywav Treatment Period (Period 2 to 5) using Weekly Lookback of Daily Diary.

The ESS is a self-administered questionnaire with 8 questions (Johns 1991, Johns 1992). Respondents rate on a 4-point scale (0-3) their usual chances of dozing off or falling asleep while engaged in eight different activities. Most people engage in those activities at least occasionally, although not necessarily every day. The ESS total score (the sum of 8 item scores, 0-3) can range from 0 to 24. Higher ESS total scores are associated with higher sleep propensity in daily life, also referred to as 'daytime sleepiness'. The ESS has been validated in several conditions, including narcolepsy (Johns 1994).

The FOSQ-10 (Chasens 2009) is a self-administered questionnaire designed to assess the impact of daytime sleepiness on activities of daily living. It consists in 10 items measuring the participant's general productivity, activity level, vigilance, and intimacy and sexual relationships. For each item, participants are asked to rate the level of difficulty in completing an activity on a 4-point Likert scale, from 1 "Yes, extreme" to 4 "No"). From the FOSQ-10 a total score is calculated: a higher score indicates better functional status. The FOSQ-10 is a reduced version of the original FOSQ-30. The FOSQ-10 was tested and found to be a psychometrically strong instrument performing similarly to the long version.

The BC-CCI was developed to measure cognitive complaints in individuals with Major Depressive Disorder (MDD). It is a 6-item self-report measure that asks respondents to rate problems with specific cognitive symptoms over the past 7 days. A four point scale (0 "Not at all" to 3 "Very much") is used to rate each item. The total score (ranges from 0 to 18) that is generated assesses domains of memory, concentration, trouble expressing thoughts, word-finding, and problem solving. Higher scores indicate greater severity of cognitive impairment, with four established classification ranges for the BC-CCI total score: 0 to 4 = "broadly normal"; 5 to 8 = "mild" cognitive complaints; 9 to 14 = "moderate" cognitive complaints; and 15 to 18 = "severe" cognitive complaints. Three additional items that ask about how these symptoms impact work, relationships and social/recreational activities are also included to provide further information on the nature of functional impairment.

The PGI-C is a series of self-administered questions designed to measure the meaningfulness of change in symptoms following an intervention. The PGI-C is used to assess the change in excessive daytime sleepiness, cataplexy, and short- and long-term nausea since the transition from Xyrem to Xywav. It is a 7-point Likert-type rating scale from 1 = very much improved, 2 = much improved, 3 = minimally improved, 4 = no change, 5 = minimally worse, 6 = much worse, to 7 = very much worse. The score is the sum of responses to each of the answer choices.