I just noticed that usually when I say 'ridden' or sometimes 'written', I don't let the air escape around my tongue as 'duh' or 'tuh' but instead keep it sealed and do something at back of my nose to let it escape suddenly to say 'dn' or 'tn'. (I can say these bits with my mouth fully closed.)
I'm pretty sure I'm not using the back of my tongue for this - I can still do it if I poke my tongue fully out and bite it to keep it out. It also feels higher up than a glottal stop.
What are these called? I looked up nasal consonants, and only found ng, n, and m.