charles barnhoorn , 20 , was discovered dead at the family home in devon .
weekend before he had took hundreds of canisters of ` hippy crack '
an inquest recorded that his death was self inflicted from asphyxiation .
his mother susan has called for the sale of nitrous oxide to be controlled .
for confidential support on suicide matters in the uk , call the samaritans on 08457 90 90 90 , visit a local samaritans branch or click here .