As the editor of Secr waterford1 confirms (p. 326), this term is not attested elsewhere, but seems plausible as the product of the adjective peisant1 followed by a -esce suffix.
s.
1pathol.med.feeling of heaviness, sluggishness of movement:
(
1266-1300; MS: c.1300
)
Les signe de mal estomak sunt pessanteche de cors, perresce, face descoloree [...]
240.S34.42
[peisantesce] (1266-1300)