Does "to spike" imply something plummets after skyrocketing?

When used in the sense of "a rapid upward change of a measure from a prior rate or value" the phrase "to spike" does not always entail a similarly rapid change back down.

Consider this example:

"The average cost for regular, unleaded gas is expected to spike to $2.49 per gallon this year, up from $2.13 in 2016. That significant uptick is in marked contrast to the steady price drops consumers have mostly seen over the past four years." http://www.usatoday.com/story/money/2017/01/03/gas-prices-expected-spike-2017/96111548/

Here "to spike" just means "significant uptick" with no anticipation of when the value will lower again.

That being said, "spikes" or "a spike" would tend to convey the sense of a short term deviation with a return to a lower value. If I were to say: "The newspaper's website saw a spike in traffic when the mayor was arrested." the implication is clear that this is a short term increase.

One needs to note that "spike" has several definitions:

• A pointed object, such as a large nail
• The metaphorical use of "pointed object", as with a "spike" in a graph
• To surreptitiously add drugs or alcohol to a drink
• To drive a volleyball or (American?) football downward sharply
• To "liven up" a party or meeting (often used as "spike up")
• To increase sharply

If gas prices "spike" that generally implies a sudden increase, as suggested by the last definition above. While often there is eventually a downward trend sometime later, that is not implied/required by the word "spike".