Complex sentence: Lynsey is told that Cheryl has sedatives in her system although she is "completely flummoxed" as to how this happened as she does not not consider that Silas would have wanted to hurt Cheryl.
Split into simpler sentences: Lynsey is told that Cheryl has sedatives in her system. Hassan disclosed that Lynsey is "completely flummoxed" as to how Cheryl came to have sedatives in her system and does not not consider that Silas would have wanted to hurt Cheryl.