concentrate (focus one's attention or mental effort on a particular object or activity)

induce (bring about or cause something to happen)

replenish (restore something to a former level or condition)

chronic (continuing for a long time or constantly recurring)

condition (an illness or other medical problem)

insomnia ( inability to sleep)

symptom (a change which shows that something bad exists)

mechanism (a process or system that is used to produce a particular result)

slumber (sleep)