Some believers experience the 'mountain top' feeling for weeks after they accept Christ as Lord and some don't. However, salvation is not about feelings, it is about faith. The Bible tells us that we are 'saved' when we confess our sins to God and put our trust in Jesus{1 John 1:9}. Therefore, even when we don't 'feel' saved we know that we are because of God's word {John 1:12}
Some Christians tend to question their salvation when they are going through tough times. However, adverse circumstances do not mean that we are unsaved. According to James 1:2-4 trials develop perseverance, and perseverance fosters maturity. When we experience obstacles in life it is because God wants to shape our character, make us more like Christ, and take us to another level. {Romans 8:28}