All of a sudden the water in my bathroom sink has gone done to trinklng when on a full force. Does any one have any suggestions as to what it can be.? Thanks in advance for helping me.

If the bathroom sink is the only one with low water and it is both hot and cold that is a problem, I would start by checking the screen on the end of the faucet. Most have a screen, or aerator, that can become clogged with rust and debris. You will have to unscrew this filter and may require the use of a pair of pliers. Try to put a piece of cloth around the screen to prevent the pliers from scratching the finish. When removed, take the pieces out and inspect. You may need a needle to clear some of the pieces of rust, etc. Reassemble the same way as before and re-install.
If that doesn't do it, you may have some debris trapped in the inner workings of the faucet assembly that will require more work.
Also, check the shut off valve. Make sure it is fully open.

While aerator is removed, turn faucet on. If pressure is normal, problem solved.

Good luck

Chuck