Can muscle tension/anxiety cause enlarged lymph nodes in neck? or submandible lymph region?

No: However, if you tend to be over-anxious and you're a young adult, you'll start noticing the lymph nodes that everybody has in their necks. A dangerous node is obviously very abnormal clinically. You need to learn to ignore the ones that aren't fixed to surrounding structures, stony-hard / tire-rubber hard, and not deforming. Please talk with your physician about overcoming these kinds of fear

Realize: We all have lymph nodes around the neck and jaw line. The ? is when a normal node becomes "pathologic", which can occur from any cause of local inflammation which drains to the node(s) in question. Muscle tone and/or anxiety alone should not cause pathologic nodes, unless there is some inflammatory condition driving muscle tone or anxiety issues. If you are worried have your doc check it out.