2.5 year old night terrors?

Hey Mummas,
I am having a bit of trouble with my 2.5 year old who seems to be having night terrors or something similar. He has always been a good sleeper but the past week or two he has been getting out of bed at about 2/3 in the morning and coming into our bed. We put him back and usually he will sleep til the morning then. However last night, he woke in a very upset state, screaming, waking his younger brother, was in a bit of a hot sweat, quite shaken and jumpy. We asked him what was wrong and he said he was scared of the snail!!! What snail?!?! He used to love snails, always talking about them and looking for them in the garden etc but then this happened! We are so confused, there was nothing in his bed or room out of the ordinary. This morning I changed all his bedding with him there to show him that there was nothing there, but he is still saying hes scared. Not looking forward to tonight!! Has anything similar happened to anyone else? So strange and really affecting the rest of us in the house. I just want to comfort him and make it right but have no idea what I can do for him.