Slepiness or Sleepiness: How To spell?
The word Slepiness is misspelled against Sleepiness, a noun meaning "The quality or state of being sleepy."
Sleepiness has double "ee" is mispronounced as "e"Remember double 'EE' in between the strings Sl & piness which should not be misspelled with single 'E'
Wrong Spelling:  Sl-e-piness  Correct Spelling:  Sl-ee-piness 
Find more wrongly spelled words of Sleepiness to spell it well.