Brief Answer:
it could cause problems

Detailed Answer:
Hello,

blood pressure fluctuations may cause problems to patients with severe heart disease (advanced heart failure). Heart failure makes the heart less capable to cope with its tasks. When the blood pressure rises, the load on the heart rises accordingly. In some patients it may lead to pulmonary edema, which is a life-threatening situation.

So it's the rise that's more dangerous, most of the times. A sudden drop in blood pressure could cause faintness but it's not so common. Please keep in mind that the blood pressure may rise because of various reasons like psychological stress, pain, etc. When the reason that caused the rise, is no longer present, then the blood pressure will return to normal. This is not so dangerous usually.

I hope you find my comments helpful!
You can contact me again, if you'd like any clarification or further information.

Kind Regards!

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