Mold allergy can cause hives,ithching,rashes and respiratory symptoms and sometimes dizziness;but it can’t cause excessive sleepiness without any of these symptoms associated.
Causes of excessive sleepiness are sleep-wake cycle disorder like in night shifts, sleep apnea and other sleep-related breathing disorders, psychiatric disorders like depression and schizophrenia,diabetes,obesity,restless leg syndrome,use of drugs or alcohol and narcolepsy(Abnormal sleep disorder leading to excessive daytime drowsiness). Kleine-Levin syndrome is present in about three times more males than females, but it is a very rare syndrome and can be a cause of hypersomnia or excessive sleepiness.
I feel that you should get your husband evaluated by a sleep specialist and find out the confirmatory diagnosis.Treatment will depend upon the diagnosis.
Take care and regards.