This is something i'm sure we can all relate to. As humans our iman goes up and down over time. It is our job to catch ourselves each time we notice our faith decreasing as to not fall into too deep of a whole. The best remedy for weak iman is to read Quran and to constantly be in a state of dhikr. These are the signs that we should all be cautious of.
1)-Committing sins and not feeling any guilt.
2)-Having a hard heart and no desire to read the Quran.
3)-Feeling too lazy to do good deeds, e.g. being late for salat
4)-Neglecting the Sunnah.
5)-Having mood swings, for instance being upset about petty things and bothered and irritated