Chlamydia does not occur in oral sex; yes there have been some cases, but it rarely rarely hardely ever happens, that its something you shouldn't worry about.
You should worry if anything on NGU, gonorrea, syphils, which are LOW low risk from the encounter of recieveing oral sex.
The chances of getting an STD from recieving oral sex is low risk but not zero risk.
It is INCORRECT to say, "the thing your most likely to catch is herpes". You will most likely catch (again if anything) NGU. True you can get genital herpes from someone with oral herpes, but its a low risk activity as well.
Chlamydia does occur and herpes is the thing your most likely to catch.
Definitely. A lot of people believe that stds will be at the same level as unprotected vaginal and anal sex. However, most experts believe oral sex is almost safe sex. The only things to worry about is NGU and Gonorrhea. Chlamydia does not occur in oral sex and without sores or chancres, syphilis and herpes are even lower. It is usually guilt and anxiety that manifest physical symptoms.