Vein Bulging On Left Wrist. Slight Sensation Felt, Abnormal Event. What Is It?

Hello. Thank You for the opportunity to ask you this question. I am a 57 y.o. white male of Italian descent. Good stress test results as of January this year. I can provide more history if needed. Earlier this evening, while stringing a guitar, I felt a slight sensation, not painful, but noticeable, at my left wrist . I looked down at it and a 4 or 5 inch length of the vein facing upward when my palm was facing inward/ thumb up, was bulging or gorged. It ran from the base of the meaty thumb/wrist junction up the arm where it appears as if it meets with other blood vessels. My veins are normally prominent, however this is an abnormal event. It varies in thickness (volume?) on its own. I can cause it to revert to a normal appearance by raising my arm. Any thoughts or suggestions would be appreciated. I don t want to under or over react. Thanks again. John