There is a perception mentioned in earlier posts that I simply don't understand and which is really concerning.

To decide not to safeword because I want to please Him/Her and feel I don't want to disappoint Him is quite simply Not my decision to make!

If I am instructed that I should tell Him if I am uncomfortable... My duty is to obey... Deciding to keep quiet is simple disobedience. This Is Not about MY will, but His. Often this discomfort was His plan all along and things continue.

When that moves closer to the point of not being able to handle something, I must tell Him, if I am able to (not gagged or deep in subspace) Once again, I may not simply decide to keep quiet. It is not within the scope of my authority in the relationship.

Any Dominant worthy of your submission will be concerned for your safety when playing.
And believe me, even online.
In fact, online, the good Dominants will give you an out. They won't want to cause harm.

I am glad for the OP that the Dominant was in fact watching over her, but being restrained without supervision shouldn't happen.

When I just came into BDSM there was a case that made National news of a woman who was restrained and left alone for only a short time. She vomited, choked and died. It is an unsafe practice to be left alone. Period.