Snorkeling and DCI

Question:
After a deep dive requiring a decompression stop, I like to go snorkelling in between to take pictures in the reefs. Normally I snorkel down to a maximum of 12 meters. It was pointed out to me that this could aggravate the onset of Decompression Illness. Is there any truth in this statement?
I have discussed this with various people who unfortunately are not experts. I am receiving a lot of theories for and against this statement.
If you could clear this up as I believe that if there is any truth in this then I would like to point the fact out to my students. I also feel it would be of interest to the diving public if there is some truth to this statement.

Answer:
Actually there is some - at least theoretical - truth in the statement.
Also, there is some epidemiological evidence of rapid onset of cases of neurological DCI soon after a quick dive within the first 20 minutes after the ascent from a SCUBA Dive (be this a breath-hold or a second quick SCUBA plunge - say to disentangle and anchor line or the like).

The rationale is the following:
Gas bubbles are normally produced and circulating during almost any ascent after SCUBA Diving, more so if the ascent has been relatively rapid (DAN recommends to ascend from any dive at never more than 9 meters per minute) and when the dive approached or superated the no decompression limits.
Bubble production peaks normally between 10 and 30 minutes after surfacing.

During this period gas bubbles are circulating in the venous blood and, normally, are trapped and filtered out by the lungs. Most of the times - and when the gas load is not excessive - this does not produce any significant problem.

If a quick dive ( such as a breath-hold dive or a short SCUBA dive ) is done within this interval, there is the possibility that the circulating gas bubbles are compressed and reduced in volume and pass through the pulmonary filter, reaching the arterial circulation and there expanding again during the ascent, with a significant probability of tissue damage, expecially at central nervous system level .
If a dive is perfomed during this "critical" interval, it is wise to prolong the bottom time to allow for a normal redistribution of gas into the tissues (for example about 15 minutes at 10-15 meters) and then conduct the ascent as if the second dive was a continuation of the first.

A breath hold dive would not allow for this safety procedure to be respecetd and should be advised against during the first 25-30 minutes after a SCUBA dive. Obviously this does not apply to surface snorkeling and fish-watching.