First of all, you should try to figure out what causes you to have these emissions and correct the source of the problem. If possible you should always sleep on your side, not the stomach or back. If it is caused by your thoughts during the day, you should work on this aspect. If it is beyond your control you are an ones and can only daven to Hashem to protect you in the future.
While it is true that a certain degree of tuma affects the person even after immersing in the mikva until night, and this is why the first mishna in Shas says that the Kohanim who were tamei could not eat teruma until night, however this only affects teruma and korbanos. The Halacha as brought in Shulchan Aruch is that one may and must daven, say berachos and wear tefilin even if he did not go to the mikva at all, as long as he cleaned himself properly. Therefore if this happens again, you should take a shower or otherwise clean yourself well and wash your hands 3 times as you anyways would when waking up in the morning. Afterwards you have all the duties and obligations of a person who is tahor, though it is praiseworthy to go to the mikva to remove the tuma completely.