Sleep and dreams have fascinated humans since ancient times, a fascination that is reflected in medicine and the arts. Epilepsy and seizures have similarly remained a mystery for much of human history. The use of the electroencephalogram in humans triggered exploration of sleep and seizures with objective real-time information. With this data, it has become increasingly apparent that sleep and epilepsy have a very close relationship. Seizures occurring during sleep may take years to diagnose. These seizures may be missed if the patient does not remember them or may be erroneously diagnosed as a sleep event or disorder. Paroxysmal events occurring during sleep have an extensive differential diagnosis, including epileptic seizures. We offer an overview of seizures occurring mostly during sleep (including the syndromes most closely linked to sleep), emphasizing the sleep-related hypermotor epilepsy (SHE). At the same time, we review paroxysmal phenomena occurring during sleep, including selected sleep disorders, with particular emphasis on those that are often confused with sleep-related seizures. There are challenges to arrive at a timely diagnosis, but careful observation and attention to the clinical presentation help differentiate these disorders.