**Core Concept**
Imipramine is a tricyclic antidepressant (TCA) that primarily works by inhibiting the reuptake of norepinephrine and serotonin. This mechanism leads to an increase in the concentration of these neurotransmitters in the synaptic cleft, thereby enhancing their effects on the postsynaptic receptors.

**Why the Correct Answer is Right**
During treatment with imipramine, it is unlikely to occur that the patient will experience an increase in platelet aggregation. This is because the drug inhibits the reuptake of norepinephrine, which in turn activates alpha-2 adrenergic receptors on platelets, leading to decreased platelet aggregation. In contrast, the other effects listed, such as anticholinergic effects, orthostatic hypotension, and sedation, are common side effects of imipramine due to its action on various receptors and systems.

**Why Each Wrong Option is Incorrect**
**Option A:** Anticholinergic effects are a common side effect of imipramine due to its blockade of muscarinic acetylcholine receptors. This leads to symptoms such as dry mouth, constipation, and urinary retention.
**Option B:** Orthostatic hypotension is a known side effect of imipramine, particularly in the elderly, due to its alpha-1 adrenergic blocking activity, which reduces peripheral vascular resistance.
**Option C:** Sedation is a common side effect of imipramine, particularly at low doses, due to its action on the central nervous system, including the blockade of histamine H1 receptors and the inhibition of norepinephrine reuptake.

**Clinical Pearl / High-Yield Fact**
It is essential to note that TCAs like imipramine have a narrow therapeutic index, and their use requires careful monitoring of side effects, particularly in the elderly or those with pre-existing medical conditions.

**Correct Answer: D.**