1. Cheerfully irresponsible
   - carefree, devil-may-care, freewheeling, happy-go-lucky, harum-scarum 
2. Dazed from or as if from repeated blows
   "slaphappy with exhaustion"
   - punch-drunk, silly

See also: confused, irresponsible

• misdiagnosis
• misdirect
• misdirection
• misdo
• misdoubt
• mise
• mise en scène
• miseducate
• misemploy
• miser
• miserable
• miserableness
• miserably
• miserere
• misericord
• miserliness
• miserly
• misery
• misestimate
• misestimation
• misfeasance
• misfile
• misfire
• misfit
• misfortunate