Can hypomania/grumpiness occur with decreased sleep?

Yes it can. Yes, sleep deprivation can cause both irritability and mild euphoria. Studies show decreased sleep increases the amount of Dopamine in the brain, promoting an amphetamine like response. This wakefulness comes with a decrease in the brain's processing ability. Sleep loss is also associated with increased appetite, risk of stroke, and heart disease.
Yes. Everyone needs at least 7 hrs of sleep, less may affect your health.

Related Questions

Can hypomania or mania occur without decreased sleep?

Yes. They can be manifestation of sleep related problems or independent of these. Read more...
There can be trigger. Other than sleeplessness. Prescription medications are one (antidepressants, stimulants, steroids, decongestants, asthma inhalers ; antabuse) as well as caffeine ; illicit drugs. Lack of sleep, menses, head injury, ms ; infectious diseases are other causes. Psychosocial stressors may include death of loved one, divorce, loss of work, trauma ; financial problems. Read more...
Yes. While decreased sleep is a very typical symptom of (hypo) mania no single symptom is absolutely required of the state. Read more...

Can hypomania/mania occur without the decreased sleep?

Yes. Lack of sleep can bring a stable perso out of stability but so can a lot of other things like stress or schedule changes, not just sleep deprivation. Read more...
Yes, but. Decreased sleep is one of the most typical symptoms of mania and hypomania. Still, every person is unique and what's typical for most may not be true for the individual. Clinical judgement is always required, and knowledge of the entire context. Read more...