Phenylephrine found in cold medication such as lempsip stimulates the alpha₁ receptor which triggers vasocontriction and increases blood pressure. Pseudoephedrine found in sudafed stimulates the beta receptor to release noradrenaline this triggers vasoconstriction of blood vessels and slows down mucus production.

These medications elevate the blood pressure so if you already suffer with high blood pressure they are best to be avoided

Primary hypertension and essential hypertension are exactly the same thing. Initially it was thought that hypertension was essential to the proper functioning of the body hence the phrase essential hypertension.

Yes many antihypertensives can have hypotension as a side effect.  When you suddenly get up there is rush of blood to the legs and a low rate of venous return, which leads to a decrease in cardiac output and therefore a decrease in blood pressure.  Calcium channel blockers have dizziness as a major side effect as occasionally they can causes excessive vasodilatation.

Salt causes retention of water.  As we have already established high volumes of water in the body increases blood volume and therefore blood pressure.

The Food Standards Agency recommends that adults consume no more than 6g per day.  Some research has questioned whether some people are actually 'salt resistant' but this has yet to be proven

Yes during physical activity your blood pressure will increase but it will soon return to normal.  The faster it returns to normal the fitter you are.  By taking regular exercise you are making your heart stronger.  You have higher levels of vasodilatation due to a number of factors including metabolic waste build up (e.g. lactic acid) and increased body temperature.  Increase vasodilatation reduces blood volume and therefore reduces blood pressure

As a result of undertaking exercise you may lose weight which reduces the strain on your heart which also contributes to lowering blood pressure.