Bed RestHead-Down TiltWeightlessness SimulationWeightlessness CountermeasuresRestCardiovascular DeconditioningSpace FlightBedsNight BlindnessNight CareWeightlessnessOrthostatic IntoleranceLower Body Negative PressureTime FactorsPhotic StimulationCircadian RhythmSleepBed OccupancyMuscle, SkeletalSupine PositionReaction TimeMuscular AtrophyExercisePlasma VolumeAcoustic StimulationEarly AmbulationGeneralization, StimulusWork Schedule ToleranceHypotension, OrthostaticVibrationAnalysis of VarianceAdaptation, PhysiologicalSleep DeprivationHypovolemiaVisual PerceptionPhysical StimulationDiscrimination LearningImmobilizationAmino Acids, EssentialVascular CapacitanceAttentionHeart RateWakefulnessSleep StagesDiscrimination (Psychology)