Methods of increasing tonic inhibition in a subject in need thereof, for example a subject with Fragile X syndrome or Angelman syndrome are disclosed. Methods of treating secondary insomnia in a subject with a neurodegenerative disease or disorder are also disclosed. The methods can include administering the subject an effective amount of 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP) or a derivative thereof, or a pharmaceutically acceptable salt thereof, increase tonic inhibition in neurons of the subject; to increase slow wave sleep (SWS) and/or slow wave activity (SWA), normalize sleep architecture, reduce secondary insomnia, increase non-rapid eye movement (NREM) sleep, increase sleep continuity, enhance delta activity within NREM, increase or improve total sleep time (TST), increase or improve sleep efficiency, reduce total time awake (TAA), reduce number of awakenings (NWA), reduce latency to persistent sleep (LPS), or to reduce wake after sleep onset (WASO), in the subject, or any combination thereof.