English speakers sometimes nasalize vowels that precede a nasal consonant. In some cases, speakers don't fully pronounce the nasal consonant, especially when the following phoneme (after the nasal consonant) shares the place of articulation, as do /n/ and /s/ (both alveolar).
Here's a great article on this, and the most relevant quotes from it.
Nasal vowels are used in English as well, albeit in a much more run-of-the-mill way. They occur before nasal consonants, as in ‘man,’ ‘can‘t,’ or ‘then.’
There are some situations, even in more mainstream accents of English, where nasal vowels can entirely supercede an /n/ or /m/. For example, many people pronounced the word ‘can’t’ without really fully articulating the /n/, and the word ’embalm’ without the /m/. These are rather mundane observations, though. Because the following consonant in each word is in the same place of articulation as the preceding nasal, most of us barely notice the difference between ‘can’t’ with a full-on /n/ and ‘can’t’ with only a nasal vowel.
And per your question on if it's normal, I do the same thing you're asking about (not fully pronouncing the /n/) and I am a native US English speaker, so although normal is relative – it's normal to me!