Can I ask my dentist to give me fissure sealants?!

Hi, Im 18 and havent had any serious problems with my teeth until recently when I needed a tiny filling in my top molar, I was also given a fissure sealant in one molar. The grooves and pits of my molars are becoming a little deep and im scared soon enough they'll start to decay or something which will lead to a more serious problem. Before I got my recent filling at the check up the dentist said he was going to give me these sealants but when i went back for the filling he didnt mention them or do them and I wasnt sure if you can ask for this procedure or if you have to wait for the dentist to tell you, you need them. I got my filling last week and it fell out yesterday, which is really lame as i wasnt eating anything to pull the filling out, my dentist cant book me in until 3 weeks, which is a joke when i had to wait weeks beforehand to get the filling in the first place. Im wondering this so I can ask for the procedure when I go for my appointment. I am 18 and in education still so I get treatments on the nhs, would this treatment be covered by the nhs? Thanks for all answers provided