I took Lamotrigine 100 mg x 2 year ago when I had hypomania and delusions and it never made me depressed, sometimes I took higher dose because it worked really weak for me, maybe because I didnt take anything else.

It never made me feel depressed, I didnt have any side effects. If you take so low dosage like 25 mg, I dont think it can make you depressed, maybe there is another reason or maybe you are not hypomanic anymore so you want to feel like this again and miss this feeling but 25 mg x2 is really low dose.