Hi, and welcome to the board.
First let me address the all night dreaming issue you mentioned. It is not dreaming in itself that causes serotonin depletion, rather it is the stress created by not achieving deep sleep on a regular basis (sleep deprivation due to a sleep disorder, etc.). For those interested in sleep patterns, and what is healthy sleep and what is not, you can read more here:
http://www.sleepdisorderchannel.net/stages/
About the 5-HTP. First of all, I have to mention that 5-HTP and L-Tryptophan are not the same (5-HTP is a derivative and not as effective as the amino acid L-Tryptophan). You can read more about it in the link I provided above if you have not done so already. However, if you want to give the 5-HTP a try, then I recommend taking it one hour before bedtime, after your evening meal.
Your body will go through an adjustment period, and you might feel sleepier than usual, this should pass. However, if you experience any disconcerting side-effects for an abnormal length of time, please consult with your doctor. Also, please don't take 5-HTP if you are also using an MAOI or SSRI.
Continue with the good work and healthy steps you've implemented, and keep us posted.
All the best,
Anthea