Yes, you can take whatever you want. However, if you would like to know if B12 is low and causing your symptoms you need to be tested before you start. It can be useful to know where you are in the scheme of things.

Naturally in the body, our liver stores up to 5 yrs worth of extra, and so in normal people, a few months of acid blocking drug use or other depleting drug, will not harm you. But if you are initially not absorbing it, from food or have been depleting it with drugs for years, then yes, you could have no backup left.

As people age, they make less acid, and then less B12 is absorbed. If you have autoimmune disease, it may have attacked your parietal cells that make instrinsic factor, and you may have pernicious anemia. Other malabsorption may occur in Crohn's patients, or those with gluten intolerance.

People who are very low in testing, can start at 5mg a day of active B12-- called methylcobalamin -- each morning on an empty stomach. People not really low, can start at 1mg a day.

One test that offers a "hint" as to low B12, before real anemia hits (usually late in low B12 patients), is an elevated MCV --mean corpuscular volume-- in the CBC tests. Although many doctors ignore this, it can point to a need for further testing, either using serum B12 level or MMA level.

Sublingual is not necessary. Oral works fine as long as you take it on an empty stomach.

This is a link to my informational B12 thread:
http://neurotalk.psychcentral.com/thread85103.html

Methyl form is not commonly seen in local stores.
But many online places have it for very little cost:
iherb.com
vitacost
Swanson's
Puritan's Pride

It works out to pennies a day. B12 has no upper limit set for safety because it has not shown toxicity in any studies yet.
High dose oral is only absorbed 10% or less per dose.
Studies done without regard to food, have been in the 10microgram absorption range for 1000mcg swallowed.
Here is a post with two good links in it:
http://neurotalk.psychcentral.com/thread85103.html

Please take a look.