I more or less remember the plot. Probably made in early 2000s, it must be like 10 years since I saw it so 100% is older than 2010. Could be late '90es but somehow I think it was made after 2000. It is in color and barely has any effects, so I guess it is a low budget but acting and camera job were excellent.
I think it is Norwegian movie.
A group of friends go camping in forest, but not in tents or cabins but like camping trailers or something. There was like huge fire in the forest some days ago so could be they thought it's cool to camp after the fire, not sure. Seems like fire awoke some parasite bugs as they find in the forest some strange shapes or like some bugs going over corpses of small dead animals. Those small piles of moving bugs is all of effects that movie used.
Anyway, those bugs or something can infect humans and control them. Infected person knows his/her name and find their way around, but have no long term memory and behave strangely and always try to get or decieve others into infection. When one strange behaving guy was being checked by others, he opened his mouth and somebode saw inside at the throatthat that there was something that moved and hid inside the throat, so they freaked out.
I remember when only two guys and girl are left uninfected, and then one guy gets infected and starts to laugh or something, and he turns to them and say something like "What? You wanna check my throat as well?" and then opens his mouth as much as he can going towards them and they clearly see he is infected also and start to run. I remember they sleep in the forest in pitch dark scared and not knowing should they trust each other in the morning.
Anyway, it builds the tension great and you never get to see inside anyone's mouth.
No explosions nor CGi nor fighting scenes.